Document repository name limits and restrictions

[webdevpraveen]

Resolves #44518

Description

This PR adds the missing documentation for repository name limits to the "Repository limits" page (content/repositories/creating-and-managing-repositories/repository-limits.md).

As outlined in the issue, the new Repository name section now explicitly documents:

• Maximum length: The 100-character limit.
• Allowed characters: Which characters are allowed and how non-ASCII characters are automatically sanitized.
• Reserved suffixes: The restrictions regarding .git and .wiki suffixes.

These limits are fundamental when creating a repository, so I've placed the new section right before the Repository size section for logical flow.

[github-actions]

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Source	Review	Production	What Changed
repositories/creating-and-managing-repositories/repository-limits.md	fpt ghec ghes@ 3.21 3.20 3.19 3.18 3.17	fpt ghec ghes@ 3.21 3.20 3.19 3.18 3.17

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🤖 This comment is automatically generated.

[Sharra-writes]

@webdevpraveen I'm sorry, but this isn't the change that the team settled on, as noted in the issue. The issue gives the exact wording and placement we want. If you would like to open a PR that follows those guidelines, I would be happy to take a look at it.