Only limit container width on issues & MRs within fixed-width container

Only sets max-width if your layout preference is fixed.

Before	After

Closes #25907 (closed)

assigned to @fatihacet

@annabeldunstone I and the before and after screenshot table. I think we should consider making this a feature :)

I can't take credit for this. I stole the table markdown from an issue @awhildy had opened!

assigned to @annabeldunstone

And I stole the table styling from @pedroms. Agreed we should consider how to make this styling easier / a feature.

assigned to @fatihacet

merged

mentioned in commit ae51027d

Tested this locally works good. @annabeldunstone can you create a technical debt issue for the comments here?

mentioned in issue #26153 (closed)

resolved all discussions

@awhildy Maybe an Issue template?

When will this be available on gitlab.com?

Picked into 8-15-stable. Will go into 8.15.3.

removed ~149423 label

mentioned in issue #26163 (closed)

mentioned in commit 1bd3eadb

mentioned in issue #25907 (closed)