chore: support amundsen-rds == 0.0.7 for mysql_proxy in metadata_service

[xuan616]

Summary of Changes

• supported amundsen-rds == 0.0.7 for mysql_proxy.py and support sqlalchemy >= 1.4, which is a change coming from amundsen-rds.
• removed redundant package dependency for rds in setup.py

Tests

Documentation

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