feat(bigtable): enable bigtable conn pool by default

[sushanb]

Can be disabled via CBT_BIGTABLE_CONN_POOL=false.

[gemini-code-assist]

Code Review

This pull request updates the EnableBigtableConnectionPool function to enable the connection pool by default if the environment variable is unset or invalid. The feedback recommends clarifying the code comments to explicitly state the fallback behavior when environment variable parsing fails.

[gemini-code-assist]

The comment 'just fail' is ambiguous. When implementing logic that parses strings, include clear error handling for parsing failures. It is clearer to state that the code is falling back to the default behavior when parsing fails.

Suggested change

	// just fail and use bigtable conn pool
	return true
	// If the environment variable value is invalid, default to enabling the pool.
	return true

References

1. When implementing helper functions that parse strings, always use the provided string parameter and include error handling for parsing failures. For test helpers, panic can be used for unrecoverable parsing errors.