Issue:
Bug: fix(invite): set user status to invitation sent if a registered user is invited





Pull request description:

## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [ ] New feature
- [ ] Enhancement
- [x] Refactoring
- [ ] Dependency updates
- [ ] Documentation
- [ ] CI/CD

## Description
<!-- Describe your changes in detail -->
This PR will set the status of the user who has been invited but already registered with Hyperswitch as InvitationSent

### Additional Changes

- [ ] This PR modifies the API contract
- [ ] This PR modifies the database schema
- [ ] This PR modifies application configuration/environment variables

<!--
Provide links to the files with corresponding changes.

Following are the paths where you can find config files:
1. `config`
2. `crates/router/src/configs`
3. `loadtest/config`
-->


## Motivation and Context
<!--
Why is this change required? What problem does it solve?
If it fixes an open issue, please link to the issue here.

If you don't have an issue, we'd recommend starting with one first so the PR
can focus on the implementation (unless it is an obvious bug or documentation fix
that will have little conversation).
-->
Closes #3756 

## How did you test it?
<!--
Did you write an integration/unit/API test to verify the code changes?
Or did you test this change manually (provide relevant screenshots)?
-->
Local SES.
```
curl --location 'http://localhost:8080/user/user/invite_multiple \
--header 'Content-Type: application/json' \
--header 'Authorization: Bearer JWT' \
--data-raw '{
    "email": "email of the registered user“,
    "name": "name",
    "role_id": "some valid role"
}
```
```
curl --location 'http://localhost:8080/user/user/list' \
--header 'Authorization: Bearer JWT'
```
In this api response, the invited user status will be InvitationSent
```
[
    {
        "email": "invited user email",
        "name": "invited user name",
        "role_id": "merchant_admin",
        "role_name": "Admin",
        "status": "InvitationSent",
        "last_modified_at": "2024-02-21T13:37:26.847Z"
    }
]
```

## Checklist
<!-- Put an `x` in the boxes that apply -->

- [ ] I formatted the code `cargo +nightly fmt --all`
- [ ] I addressed lints thrown by `cargo clippy`
- [ ] I reviewed the submitted code
- [ ] I added unit tests for my changes where possible
- [ ] I added a [CHANGELOG](/CHANGELOG.md) entry if applicable


Testing:

Local SES.
```
curl --location 'http://localhost:8080/user/user/invite_multiple \
--header 'Content-Type: application/json' \
--header 'Authorization: Bearer JWT' \
--data-raw '{
    "email": "email of the registered user“,
    "name": "name",
    "role_id": "some valid role"
}
```
```
curl --location 'http://localhost:8080/user/user/list' \
--header 'Authorization: Bearer JWT'
```
In this api response, the invited user status will be InvitationSent
```
[
    {
        "email": "invited user email",
        "name": "invited user name",
        "role_id": "merchant_admin",
        "role_name": "Admin",
        "status": "InvitationSent",
        "last_modified_at": "2024-02-21T13:37:26.847Z"
    }
]
```

Patch:
diff --git a/crates/router/src/core/user.rs b/crates/router/src/core/user.rs
index 54fbecc64f3..96753236c1c 100644
--- a/crates/router/src/core/user.rs
+++ b/crates/router/src/core/user.rs
@@ -666,7 +666,13 @@ async fn handle_existing_user_invitation(
             merchant_id: user_from_token.merchant_id.clone(),
             role_id: request.role_id.clone(),
             org_id: user_from_token.org_id.clone(),
-            status: UserStatus::Active,
+            status: {
+                if cfg!(feature = "email") {
+                    UserStatus::InvitationSent
+                } else {
+                    UserStatus::Active
+                }
+            },
             created_by: user_from_token.user_id.clone(),
             last_modified_by: user_from_token.user_id.clone(),
             created_at: now,