Repository: dynaconf/dynaconf (python)

Issue:
Support parameter abbreviation on Flask and Django plugins
### Discussed in https://github.com/dynaconf/dynaconf/discussions/847

<div type='discussions-op-text'>

<sup>Originally posted by **kssflow** December 27, 2022</sup>

Hello everyone! (happy new year in advance 🎉)
First of all, really appreciate for maintaining this invaluable, literally amazing open source project. 👏😸 


I consult to Flask documentating saying "dynaconf" is one of (recommended) solutions for configuration management.
So I have given a shot to this library with carefully reading the docs and typing code.
But the more I do my best to handle(solve) the problem the more I totally lost in frustration.

For example, the doc says `envvar_prefix` makes the prefix of environment variable. 

```python

from flask import Flask
from dynaconf import FlaskDynaconf

app = Flask(__name__)
FlaskDynaconf(app, envvar_prefix="PEANUT")

```

It doesn't work... but if I change the `envvar_prefix` to `envvar_prefix_for_dynaconf`, it works finally.

**Does doc is wrong?**
(I hope that it's not doc but me makes problem) 
If docs are wrong, there seems to be INCONSISTENCY related to Flask Integration part... 

python code

```python

# main.py
# working code

from flask import Flask, render_template, current_app
from dynaconf import FlaskDynaconf

app = Flask(__name__, template_foler=templates")
FlaskDynaconf(app, 
   load_dotenv=True, 
   envvar_prefix_for_dynaconf="DAMNIT"  # 🔴 doc say "envvar_prefix" but that doesn't work 
)

@app.route("/", methods=["GET"])
def index():
    settings = current_app.config
   return render_template("index.html.jinja", settings=settings")

```

jinja(html) code

```html

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <h1>HELP ME!!</h1>
    <div style="border: 1px solid red; width: 100px; height: 100px;">
        {{ settings.APPNAME }}
    </div>
    <div>
        {% if settings %}
            <dl>
            {% for key, value in settings.items() %}
                <dt>{{ key }}</dt>
                <dd>{{ value }}</dd>
            {% endfor %}
            </dl>
        {% endif %}
    </div>
</body>

</html>

```
 
.env
```bash

FLASK_APPNAME=APP NAME FROM FLASK_APPNAME
DAMNIT_APPNAME=APP NAME FROM DAMNIT_APPNAME

```

🟢 results with `envvar_prefix_for_dynaconf=DMANIT`

<img src="https://user-images.githubusercontent.com/108768169/209649708-c4b8df8d-3166-40cd-87ea-6114666a5aa2.png"
 height="500px" width="500px"/>

🔴  results with `envvar_prefix=DMANIT`
<img src="https://user-images.githubusercontent.com/108768169/209649823-6bdd2878-1ec6-4abd-a10b-53f5d9ab8c71.png"
 height="500px" width="500px"/>


Thanks in advance.
Again, really thanks for maintaining and evolving this wonderful project!
 
Best regards.</div>

Pull request description:
Fix - Add support for lowercase `envvar_prefix` in DynaconfFlask (Fix #848)

Patch:
diff --git a/dynaconf/contrib/flask_dynaconf.py b/dynaconf/contrib/flask_dynaconf.py
index a305194..9fb2487 100644
--- a/dynaconf/contrib/flask_dynaconf.py
+++ b/dynaconf/contrib/flask_dynaconf.py
@@ -93,12 +93,12 @@ class FlaskDynaconf:
                 "install it with: pip install flask"
             )
         self.kwargs = {k.upper(): v for k, v in kwargs.items()}
-        kwargs.setdefault("ENVVAR_PREFIX", "FLASK")
-        env_prefix = f"{kwargs['ENVVAR_PREFIX']}_ENV"  # FLASK_ENV
-        kwargs.setdefault("ENV_SWITCHER", env_prefix)
-        kwargs.setdefault("ENVIRONMENTS", True)
-        kwargs.setdefault("load_dotenv", True)
-        kwargs.setdefault(
+        self.kwargs.setdefault("ENVVAR_PREFIX", "FLASK")
+        env_prefix = f"{self.kwargs['ENVVAR_PREFIX']}_ENV"  # FLASK_ENV
+        self.kwargs.setdefault("ENV_SWITCHER", env_prefix)
+        self.kwargs.setdefault("ENVIRONMENTS", True)
+        self.kwargs.setdefault("LOAD_DOTENV", True)
+        self.kwargs.setdefault(
             "default_settings_paths", dynaconf.DEFAULT_SETTINGS_FILES
         )
 


Test patch:
diff --git a/tests/test_flask.py b/tests/test_flask.py
index fbd40d1..9ddb2c2 100644
--- a/tests/test_flask.py
+++ b/tests/test_flask.py
@@ -142,3 +142,25 @@ def test_flask_with_dot_env():
 def test_flask_dotenv_cli():
     with flask_app.test_client() as client:
         assert client.get("/test").data == b"hello flask"
+
+
+def test_setting_instance_options_works_case_insensitive():
+    """
+    assert that dynaconf options (that are modified by FlaskDynaconf)
+    can be set by the user in a case insensitive manner. see #848
+    """
+    app = Flask(__name__)
+    FlaskDynaconf(
+        app,
+        envVar_prefix="MYPREFIX",
+        eNv_swItcHer="MY_ENV_SWITCHER",
+        enViroNments=False,
+        lOaD_dOtenv=False,
+    )
+    assert app.config.envvar_prefix_for_dynaconf == "MYPREFIX"
+    assert app.config.env_switcher_for_dynaconf == "MY_ENV_SWITCHER"
+    assert app.config.environments_for_dynaconf is False
+
+    # oddly, using '_for_dynaconf' won't work, altough
+    # the option functionality seems to work as expected
+    assert app.config.load_dotenv is False