feat: Add OpenAPI

[provokateurin]

Closes #3208
This is a "breaking" change to the API, but since it was not usable before due to CSRF restrictions it doesn't matter.
While working on this I also had to cleanup a lot of the internal typings which resulted in this relatively large change for adding OpenAPI.
If this is too big please let me know and I will try to split it up.

[provokateurin]

I will try to extract some of the changes into separate PRs to get them merged first and then come back to this PR.

[provokateurin]

I removed everything not strictly necessary to implement this. Some improvements can just be done later, like nextcloud/openapi-extractor#172.

[provokateurin]

The Cypress failure is not related to the changes, I get the same errors on master.

[come-nc]

Why removing all the id indexing, is that so bad?
Also, why the snake_case on string ids, do we have a convention about that in OCS?

[provokateurin]

Why removing all the id indexing, is that so bad?

Not really, but I just removed it because it is never used.
I prefer a list strongly over array if possible, due to the ambiguities that can happen.
I can also revert it, if you really don't like it.

Also, why the snake_case on string ids, do we have a convention about that in OCS?

No, I just wanted to make them all consistent.
I personal prefer snake_case for JSON, but we can also go with camelCase.

[susnux]

prefer a list strongly over array if possible, due to the ambiguities that can happen.

True, I think array caused really some unwanted issues :(

I personal prefer snake_case for JSON, but we can also go with camelCase.

I think we use camelCase for both PHP and JS variables and for JS working with camelCase JSON is more convenient. So if we somewhen might consider a codestyle also JSON camelCase would be nice

[provokateurin]

I think we use camelCase for both PHP and JS variables and for JS working with camelCase JSON is more convenient. So if we somewhen might consider a codestyle also JSON camelCase would be nice

Ok, fair enough :)

[provokateurin]

Why removing all the id indexing, is that so bad?

Also the code on the frontend side was very hacky in this regard, it is a lot better now.

[provokateurin]

Depends on #3407 and nextcloud/openapi-extractor#181.
No breaking changes anymore, but also very ugly typing 🙈

[provokateurin]

All depending PRs are merged, so this is finally ready.

[provokateurin]

Still waiting for a review from @come-nc before merging to ensure I addressed all previous problems.

[provokateurin]

Thanks a lot everyone! 🎉