feat(web-modeler): add git-sync self-hosted part

[JacobiCamunda]

Description

Add documentation part when using self-hosted GitHub instances (See PR). We will release a release-candidate for 8.6 today so that a customer can already run some tests, and it should be released somewhere today or tomorrow.

When should this change go live?

• This is a bug fix, security concern, or something that needs urgent release support.
• This is already available but undocumented and should be released within a week.
• This on a specific schedule and the assignee will coordinate a release with the DevEx team. (apply hold label or convert to draft PR)
• This is part of a scheduled alpha or minor. (apply alpha or minor label)
• There is no urgency with this change and can be released at any time.
• This will be part of a release-candidate (released today 20.11.24)

PR Checklist

• My changes are for an already released minor and are in /versioned_docs directory.
• My changes are for the next minor and are in /docs directory (aka /next/).

• My changes require an Engineering review, and I've assigned the Engineering DRI or delegate.
• My changes require a technical writer review, and I've assigned @camunda/tech-writers as a reviewer.

[jfriedenstab]

👍🏻

[JacobiCamunda]

@conceptualshark, I also added an alternative to also use Application ID instead of client ID in the docs. Please give me another round of review for that if you want and merge if everything is good to go 🙂

[conceptualshark]

A small suggestion, and I do think some of the wording changes suggested for the note could be helpful, but both are non-blocking and I am good with where this PR is!

[JacobiCamunda]

Could someone approve this again so it can be merged, @jfriedenstab or @conceptualshark? I forgot about this because I enabled auto-merge, but it wasn't auto-merged because of a missing approval.

[mesellings]

Not checked content, approving to unblock as per request from @JacobiCamunda 👍