Add sqlcommenter example to docs

[tammy-baylis-swi]

Description

Adds new "sqlcommenter" example to core repo docs/examples, which is linked from otel.io Python > sidebar "Examples". The sqlcommenter implementation is actually throughout opentelemetry-python-contrib, but docs/examples already includes an accessible Django example so I think this is a fair location. Contrib repo is also being updated in other PRs linked to open-telemetry/opentelemetry-python-contrib#3162.

Partially fixes open-telemetry/opentelemetry-python-contrib#3162

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

For the readme/readthedocs:

1. Virtualenv in Python 3.11
2. tox -e docs
3. Check local build in docs/_build/html/examples/sqlcommenter/README.html

For the new code example: followed the readme instructions

Does This PR Require a Contrib Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[JWinermaSplunk]

LGTM!