Allow long group description (backend: increase limit)

What does this MR do and why?

There were couple of issues around UI project description limitation to 250 chars. One of them !82812 (merged) was lately merged into 14.x release.

This MR includes similar change for Gitlab groups. Gitlab group as container of projects usually come with description which contain links to important group's content. In reality limitation downto 250 characters is really annoying and bothers multiple people on our site (gitlab.ics.muni.cz).

There is an actual limit of 2000 imposed by the backend. If one tries to save a group description longer than 2000 characters a warning will appear after clicking Save changes.

This MR as minimal change improves UI experience.

Related issue: Increase group description length from 250 char... (#416146 - closed).

The change is split into two separate MRs:

• frontend !132451 (merged)
• backend (this one) !132920 (merged)

Allow long group description (backend)

In the General Settings page one can add an optional group description. Increase actual limit of 255 to 2000 characters in the backend.

Changelog: changed

Screenshots or screen recordings

See !132451 (merged) for details.

How to set up and validate locally

See !132451 (merged) for details.

MR acceptance checklist

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