Validate list LENGTH queries with validator

[ml-evs]

As above.

Also tweaks the test for bad versions by hitting /v1234/info instead of a landing page.

[JPBergsma]

I did not see anything wrong with this code, but we have to at least prevent the triggering of the error we are currently getting for LENGTH queries on the structure features. Although, I think it would be better if we could support the LENGTH operator in a more universal manner. For MongoDB this should be possible with the size operator:
db.structures.find( {"property_name": { $size: 3 } } )

[ml-evs]

I did not see anything wrong with this code, but we have to at least prevent the triggering of the error we are currently getting for LENGTH queries on the structure features. Although, I think it would be better if we could support the LENGTH operator in a more universal manner. For MongoDB this should be possible with the size operator: db.structures.find( {"property_name": { $size: 3 } } )

We already do this generically for MongoDB but Elastic is causing the problem, simply because structure_features isn't really indexed as a list field. We should at least get it to return a nice error (501 Not Implemented) and probably allow that through the validator.

[codecov]

Codecov Report

Merging #1637 (c86b126) into master (1713044) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1637   +/-   ##
=======================================
  Coverage   91.04%   91.04%           
=======================================
  Files          74       74           
  Lines        4578     4580    +2     
=======================================
+ Hits         4168     4170    +2     
  Misses        410      410           

Flag	Coverage Δ
project	91.04% <100.00%> (+<0.01%)	⬆️
validator	90.93% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
optimade/validator/config.py	100.00% <ø> (ø)
optimade/validator/validator.py	83.75% <100.00%> (+0.05%)	⬆️

[ml-evs]

If you're good with this now @JPBergsma I think I will merge and release to get this up on the dashboard!