Load manifest.json values dynamicly

What does this MR do and why?

Fixes partially #375708 (closed)

Loads text values in manifest.json dynamicly from appearance settings

followup MR => !104582 (merged)

Adds short_title attribute to appearance API => was moved to !106979 (merged)

Screenshots or screen recordings

manifest.json in browser:

How to set up and validate locally

1. Open your local GitLab instance
2. Click f12 and inspect manifest.json in application tab
3. You should see default values for the titles, logos and so on
4. Change your Appearance settings as explained here, for example: title, short_title, description
5. Reload your browser and recheck the manifest
6. You should see the new values.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.

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