Add Lambda function that deletes test Lambda functions (#2960)

Lambda function that deletes all test lambda functions (prefixed with `test_`) that have been created during CI runs. * Lambda function that deletes test Lambda functions. This function is run every Sunday and it is monitored in the `sentry-python` project on Sentry.io with the Crons feature and it is also emitting metrics on how many functions it deletes in each run. 
---------

Co-authored-by: Ivana Kellyerova <ivana.kellyerova@sentry.io>

scripts/aws_lambda_functions/README.md

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+aws_lambda_functions
+====================
+
+In this directory you can place AWS Lambda functions that are used for administrative tasks (or whatever)

scripts/aws_lambda_functions/sentryPythonDeleteTestFunctions/README.md

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+sentryPythonDeleteTestFunctions
+===============================
+
+This AWS Lambda function deletes all AWS Lambda functions in the current AWS account that are prefixed with `test_`.
+The functions that are deleted are created by the Google Actions CI checks running on every PR of the `sentry-python` repository.
+
+The Lambda function has been deployed here:
+- AWS Account ID: `943013980633`
+- Region: `us-east-1`
+- Function ARN: `arn:aws:lambda:us-east-1:943013980633:function:sentryPythonDeleteTestFunctions`
+
+This function also emits Sentry Metrics and Sentry Crons checkins to the `sentry-python` project in the `Sentry SDKs` organisation on Sentry.io:
+https://sentry-sdks.sentry.io/projects/sentry-python/?project=5461230

scripts/aws_lambda_functions/sentryPythonDeleteTestFunctions/lambda_function.py

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+import boto3
+import sentry_sdk 
+
+
+monitor_slug = "python-sdk-aws-lambda-tests-cleanup"
+monitor_config = {
+    "schedule": {
+        "type": "crontab",
+        "value": "0 12 * * 0", # 12 o'clock on Sunday
+    },
+    "timezone": "UTC",
+    "checkin_margin": 2,
+    "max_runtime": 20,
+    "failure_issue_threshold": 1,
+    "recovery_threshold": 1,
+}
+
+
+@sentry_sdk.crons.monitor(monitor_slug=monitor_slug)
+def delete_lambda_functions(prefix="test_"):
+    """
+    Delete all AWS Lambda functions in the current account
+    where the function name matches the prefix
+    """
+    client = boto3.client("lambda", region_name="us-east-1")
+    functions_deleted = 0
+
+    functions_paginator = client.get_paginator("list_functions")
+    for functions_page in functions_paginator.paginate():
+        for func in functions_page["Functions"]:
+            function_name = func["FunctionName"]
+            if function_name.startswith(prefix):
+                try:
+                    response = client.delete_function(
+                        FunctionName=func["FunctionArn"],
+                    )
+                    functions_deleted += 1
+                except Exception as ex:
+                    print(f"Got exception: {ex}")
+
+    return functions_deleted
+
+
+def lambda_handler(event, context):
+    functions_deleted = delete_lambda_functions()
+
+    sentry_sdk.metrics.gauge(
+        key="num_aws_functions_deleted", 
+        value=functions_deleted,
+    )
+
+    return {
+        'statusCode': 200,
+        'body': f"{functions_deleted} AWS Lambda functions deleted successfully."
+    }