Preserve footnote link ids

Closes #64645

See merge request gitlab-org/gitlab-ce!30790

Prevent excessive sanitization of AsciiDoc ouptut

Closes #63298

See merge request gitlab-org/gitlab-ce!30290

Banzai - avoid redis if attr is in DB cache

See merge request gitlab-org/gitlab-ce!30334

When cache_collection_render runs we end up reading and writing
things to redis even if we already have the rendered field cached
in the DB. This commit avoids using redis at all whenever we have
the field already rendered in the DB cache.

Adds GFM Pipline filters to insert a placeholder in the generated
HTML from GFM based on the presence of a metrics dashboard link.

The front end should look for the class 'js-render-metrics' to
determine if it should replace the element with metrics charts.
The data element 'data-dashboard-url' should be the endpoint
the front end should hit in order to obtain a dashboard layout
in order to appropriately render the charts.

Enable AsciiDoc syntax highlighting (using Rouge)

Closes #32635

See merge request gitlab-org/gitlab-ce!29835