Added ability to access mongo oplog via a proxy

[pratyus]

Fixes #390

Added a new flag --is_oplog_proxy which tells the mongo connector to access oplog via the URI passed in. mongo_connector does not connect to individual shards directly to access mongo oplog.

mongo-connector -m <IP_ADDRESS>:<PORT> -a <USER> -p <PASS> --ssl-ca-certs=path/to/.pem -t <ELASTIC_DESTINATION> -d elastic2_doc_manager --is_oplog_proxy=True

[Imran-imtiaz48]

Review:
The code snippet demonstrates the configuration of MongoDB client options, including timezone awareness and proxy settings for oplog access. The tz_aware attribute is correctly initialized based on the provided keyword arguments, indicating whether timezone-aware functionality is required. Similarly, is_oplog_proxy is set to determine if the connection is via a MongoDB oplog proxy.
The add_option method is utilized to configure command-line interface (CLI) options for these settings. The help descriptions for is_oplog_proxy are clear and accurately describe its purpose for distinguishing between direct and proxied oplog access.
Recommendation:
To enhance clarity and maintain consistency, consider the following adjustments:

1. Consistent Terminology: Ensure that terminology is consistent throughout the code and documentation. For example, the description for is_oplog_proxy should be aligned to avoid confusion (e.g., use "proxy with access to mongo oplog.rs" consistently).
2. Documentation: Add comments or docstrings to the add_option function to explain its purpose and parameters. This will help other developers understand how to use and extend this function.
3. Code Formatting: Verify that there are no unintended spaces or formatting issues. For instance, ensure that the indentation and alignment are consistent to improve readability.
4. Error Handling: Consider implementing validation or error handling for the options being set. For example, check if tz_aware and is_oplog_proxy receive valid values and handle any potential exceptions that may arise.