RFC: migration to the new Lua-based website gallery export module

Is your feature request related to a problem? Please describe.

I created a new website gallery export module to replace the current module based on photoswipe. This raises the question how to migrate from the old to the new gallery. The next release comes with system-wide Lua scripts, which provide the new gallery export module for all users.

The new one consists of a Lua script and some static data (HTML/CSS/Javascript). It is rewritten from scratch does not share any code or files with the old gallery. I has all features of the old gallery, plus some new ones.

I prepared a branch that removes the code of the old gallery.

Describe the solution you'd like

Both website gallery export modules could co-exist for a certain time. The new one will be called "webseite gallery (new)" in the export settings. Users can use both export modules. At some point in the future, the old module can be removed. If a user has a major issue with the new export module, he/she can still use the old one.

Alternatives

The old export module will be removed now and the new module will be shown with the same name "website gallery", providing only the new export module for users.

Additional context

If no action is taken, both export modules will be available in the next release.

No file or test is named. Start by reviewing the prepared branch that removes the old gallery and comparing the current and new website gallery export modules in the export settings. Done means the project records and implements a decision on whether both modules coexist temporarily or the old module is removed immediately.