Ruby on Rails documentation updates

[modulitos]

This PR updates the Ruby docs to leverage the support Rails has recently provided for SQLCommenter. This will facilitate adoption of SQLCommenter for folks who aren't familiar with how SQLCommenter support has changed across Rails versions.

Note that the current docs are not compatible with Rails versions 7.0 and up. This PR makes the following changes to bring them up to date:

1. For Rails >=7.1, include docs about how SQLCommenter is now fully supported as the default formatter
   • Support was added in this PR, and it will be the default formatter as well (added in this PR).
2. For Rails 7.0, include docs on the PlanetScale SQLCommenter gem which is a workaround that provides SQLCommenter support for Rails 7.0
   • The Marginalia library was re-implemented natively in Rails version 7.0 (in this PR), so the current documentation that leverages a Marginalia fork will not work.

Corresponding PR in the OpenTelemetry repo: open-telemetry/opentelemetry-sqlcommenter#35

[modulitos]

Kindly pinging @sjs994 - is there anything I can do to help get this PR reviewed?

[sjs994]

Extremely sorry @modulitos. Somehow missed this PR.

Have added a reviewer to take a look at this PT.

[sjs994]

LGTM