Cache /info and /info/<entry> responses

[ml-evs]

This is a feature I want to use in the 1.2 changes, so it may as well be "backported" here ready for the final 1.1 release.

[codecov]

Codecov Report

Merging #1433 (1060331) into master (eae4846) will increase coverage by 0.01%.
The diff coverage is 94.44%.

@@            Coverage Diff             @@
##           master    #1433      +/-   ##
==========================================
+ Coverage   91.43%   91.45%   +0.01%     
==========================================
  Files          74       74              
  Lines        4392     4398       +6     
==========================================
+ Hits         4016     4022       +6     
  Misses        376      376              

Flag	Coverage Δ
project	91.45% <94.44%> (+0.01%)	⬆️
validator	90.85% <94.44%> (+0.01%)	⬆️

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

Impacted Files	Coverage Δ
optimade/server/routers/info.py	96.55% <94.44%> (+0.89%)	⬆️

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[JPBergsma]

This looks like a good change to me.