Add Managed Kafka Connect Connectors Examples

[salmany]

Note: This PR builds on top of the work in PR #13515 and should not be merged until that one is complete. The "Files changed" tab currently includes changes from the dependency.

This commit adds examples for creating Managed Kafka Connect connectors:

• MirrorMaker connector
• BigQuery sink connector
• Cloud Storage sink connector
• Pub/Sub sink connector
• Pub/Sub source connector

Description

Fixes https://b.corp.google.com/issues/430087669

Note: Before submitting a pull request, please open an issue for discussion if you are not associated with Google.

Checklist

• I have followed Sample Guidelines from AUTHORING_GUIDE.MD
• README is updated to include all relevant information
• Tests pass: nox -s py-3.9 (see Test Environment Setup)
• Lint pass: nox -s lint (see Test Environment Setup)
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• Please merge this PR for me once it is approved

[gemini-code-assist]

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[snippet-bot]

Here is the summary of changes.

You are about to add 5 region tags.

• managedkafka/snippets/connect/connectors/create_bigquery_sink_connector.py:58, tag managedkafka_create_bigquery_sink_connector
• managedkafka/snippets/connect/connectors/create_cloud_storage_sink_connector.py:61, tag managedkafka_create_cloud_storage_sink_connector
• managedkafka/snippets/connect/connectors/create_mirrormaker_source_connector.py:57, tag managedkafka_create_mirrormaker2_source_connector
• managedkafka/snippets/connect/connectors/create_pubsub_sink_connector.py:58, tag managedkafka_create_pubsub_sink_connector
• managedkafka/snippets/connect/connectors/create_pubsub_source_connector.py:58, tag managedkafka_create_pubsub_source_connector

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[glasnt]

It looks like the linting here is failing because both the managedkafka/snippets and managedkafka/snippets/connect/connectors have requirements.txt files, which causes linting to run in both locations

Google linting style requires that imports from local files are grouped separately. But when the linting is running from a parent folder, it doesn't see those local files, so the lint from the parent folder fails due to child folder local imports.

It looks like #13515 also introduced a new requirements.txt file, so there's no longer just one requirements file for the whole snippets folder.

Since this PR adds a requirements.txt file that duplicates the parent requirements.txt, I'm going to remove it from this PR. This will mean:

1. changes to this folder will cause the whole managedkafka/snippets sample collection to be tested, which might cause future issues with changes causing unrelated tests to fire

2. the imports for the test file will conform to parent linting, but look potentially "out of order"