Enhanced E2E test suite

[gmsdelmundo]

E2E Pipeline Improvements

• Streamlined what test suites are run in the Dockerfile using the new E2E_SUITES environment variable
• Added an E2E_ARGS_JSON environment variable to JSON-ify inputs
  • Currently mainly used to more easily manage multiple secret environment variables being passed into uid2-operator's E2E pipeline
• Cleaned up the private operator test suite
• Separated local-only operator tests from the main operator tests

Environment Variable Readability

• Updated environment variable names to more clearly reflect what they're used for
• Added all environment variables as constants for better inventory
• Cleaned up where different environment variables are being loaded in the test setups
• Added README documentation to clearly explain different environment variable usages

Others

• Updated outdated release pipeline