[Draft] Uniform frame processor API

[tanganellilore]

• Resolves: not opened for this type of PR

Summary

With new theming introduced on nextcloud >25, we can customize DocBaseUrl only if we use "old fashion way", adding defaults.php under /themes/<custom_theme>/ .

With this PR I simply added a getDocBaseUrl() function, that will get theming docBaseUrl config and will use for doc base url. It will fallback on the defaullt one if not found, in the same way as other function.

TODO

N/A

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• [ ] Tests (unit, integration, api and/or acceptance) are included
• [ ] Screenshots before/after for front-end changes
• [ ] Documentation (manuals or wiki) has been updated or is not required
• [ ] Backports requested where applicable (ex: critical bugfixes)