Repository: firebase/firebase-ios-sdk (language: cpp)

Issue:
[Security] Remove the example key from `FIROptions.h`
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### Step 0: Are you in the right place?


### [REQUIRED] Step 1: Describe your environment

  * Xcode version: 13.1
  * Firebase SDK version: 8.10.0
  * Installation method: `CocoaPods`
  * Firebase Component: Core
  * Target platform(s): `iOS`

### [REQUIRED] Step 2: Describe the problem
Currently, the file `FIROptions.h` includes an example key that triggers security systems. A better solution can be to describe the key and not include one.

```
/**
 * An iOS API key used for authenticating requests from your app, e.g.
 * @"AIzaSyDdVgKwhZl0sTTTLZ7iTmt1r3N2cJLnaDk", used to identify your app to Google servers.
 */
@property(nonatomic, copy, nullable) NSString *APIKey NS_SWIFT_NAME(apiKey);
```
Can be:
```
/**
 * An iOS API key used for authenticating requests from your app.
 * The key contains 39 alphanumeric digits, used to identify your app to Google servers.
 */
@property(nonatomic, copy, nullable) NSString *APIKey NS_SWIFT_NAME(apiKey);
```
#### Steps to reproduce:

Just see the file:
https://github.com/firebase/firebase-ios-sdk/blob/master/FirebaseCore/Sources/Public/FirebaseCore/FIROptions.h



Discussion / hints:

Fix patch:
diff --git a/FirebaseCore/Sources/Public/FirebaseCore/FIROptions.h b/FirebaseCore/Sources/Public/FirebaseCore/FIROptions.h
index afabbf101c2..97c5ae82527 100644
--- a/FirebaseCore/Sources/Public/FirebaseCore/FIROptions.h
+++ b/FirebaseCore/Sources/Public/FirebaseCore/FIROptions.h
@@ -32,7 +32,8 @@ NS_SWIFT_NAME(FirebaseOptions)
 
 /**
  * An iOS API key used for authenticating requests from your app, e.g.
- * @"AIzaSyDdVgKwhZl0sTTTLZ7iTmt1r3N2cJLnaDk", used to identify your app to Google servers.
+ * The key must begin with "A" and contain exactly 39 alphanumeric characters, used to identify your
+ * app to Google servers.
  */
 @property(nonatomic, copy, nullable) NSString *APIKey NS_SWIFT_NAME(apiKey);
 


Test patch: