Extend parameter `annotatedFor` on GET /mappings

[stefandesu]

We need some additional values for parameter annotatedFor on GET /mappings:

• any: has any kind of annotation
• none: has no annotations at all
• negative operator with !, e.g. !assessing: does not have annotations with that motivation

Required for https://github.com/gbv/cocoda/issues/605.

[stefandesu]

Unfortunately, there are big performance issues with the new negative assertions (none and !xyz) because it always has to go through the whole result set. There are actually two issues:

1. Sorting the results takes very long. I was able to mitigate this by moving the sorting process to a different place in the query pipeline, so it's not a problem.
2. Counting the total results of the query is actually the bigger issue for the above additions. With a big result set, it takes 30+ seconds to count the results because it has to load everything from the drive.

My current workaround for 2 is to skip counting the values and return an unreasonably big number for X-Total-Count (like 9 999 999). Not returning any total count breaks our client applications (and I couldn't find a convention to say "there are more values, but we don't know how many"), and as far as I can see, there is no disadvantage to this except that it's a fake value. I think if this is documented properly, it should be okay.

@nichtich Do you have an opinion on this?

[stefandesu]

I was able to find a different solution for counting the total results for negative assertions for annotatedFor: Count the results for the same query without annotatedFor, then subtract the results from the same query but with opposite annotatedFor. The code changes for this were a little difficult, but it seems to work very well. Closing this issue now!