Remove unions in params and delete request body

[rosesyrett]

This PR addresses two related issues:

1. Delete requests have a request body (which they shouldn't)
2. confusing union types in parameters

For the first task, the request body used to have a 'tag_or_idx' parameter which was a union of int or str. Now, I've changed my delete paths to require at least one query parameter, tag or idx. That is /a/path?tag=foo or /a/path?idx=0, which will dictate what is deleted.

Then, I decided to decouple my tag_or_idx parameters in general, mostly in the parameters of request bodies. As a result, my pydantic models for editing orientations/reflections now have separate 'tag' and 'idx' fields.

However, I have one major question about this change - is it best to include these 'tag' and 'idx' fields, which are currently in my EditOrientationParams and EditReflectionParams pydantic models for the request body, to be query parameters? This would be more in line with the new style for deleting orientations/reflections, however to me it also makes more sense for everything to be neatly bundled in the request body where appropriate.

[garryod]

Overall looks really good, a few little comments on style and readability here and there, but nothing of real significance

I would say they should be part of the query itself as they're the primary thing which is being indexed by, any supplementary data can be included in the body. Though @callumforrester may disagree