[Docs][Format] Document Run-Length encoding in Arrow columnar format

[asfimport]

Reporter: Tobias Zagorni / @zagto
Assignee: Tobias Zagorni / @zagto

PRs and other links:

• GitHub Pull Request #13333

_{Note: This issue was originally created as ARROW-16773. Please see the migration documentation for further details.}

[jorisvandenbossche]

The PR addressing this was closed because the changes were incorporated in PR #14176, so closing as duplicate of #32115