Define configuration for enabling sqlcommenter

[tammy-baylis-swi]

It would be great if there was a convention for how to enable sqlcommenter for those OTel libraries that have it implemented.

At the moment I see some Python and JS instrumentation libraries do this with a boolean, though the naming is inconsistent. Examples:

• SQLAlchemy instrumentation uses enable_commenter
• Django ORM instrumentation uses is_sql_commentor_enabled
• pg instrumentation uses addSqlCommenterCommentToQueries

If instead we had OTEL_SQLCOMMENTER_ENABLED (or similar) then this could be adopted by existing libraries and more libraries as sqlcommenter is implemented. It could also be exposed as an environment variable used in auto-instrumentation and manual instrumentation.