Metadata fields can't start with column

[theosanderson]

I guess that means that metadata fields may not start with column_ anymore? Not something for this PR but I wonder whether we should separate the technical search params from the metadata query params. Otherwise, after releasing Loculus, such a change would be considered a major breaking change.

For example, we could introduce a prefix such as $ for all technical params and then define that metadata columns may not start with $. If we want to do that, we should do it before launching the MVP as it will cause broken links.

Originally posted by @chaoran-chen in #1993 (comment)

See the whole thread - things aren't handled well for query parameters generally atm such that adding a random query param leads to a crash. Fix before launch.

[chaoran-chen]

We originally wanted to implement it before launch but didn't. How should we proceed with this? If we now implement it, it could break existing links, but I still do prefer having a clearer separation between metadata fields and technical parameters.

[theosanderson]

Despite the fact that this would be harder to change later, to me it's still a very niche concern that I would personally rank below most of our other issues