General store endpoint added

[munrojm]

This PR adds general store endpoints that can be used to store and pull different generic bits of markdown data and metadata.

[codecov-commenter]

Codecov Report

Merging #415 (fd2c967) into main (7a12d22) will decrease coverage by 0.12%.
The diff coverage is 85.71%.

@@            Coverage Diff             @@
##             main     #415      +/-   ##
==========================================
- Coverage   92.68%   92.56%   -0.13%     
==========================================
  Files          61       63       +2     
  Lines        2010     2031      +21     
==========================================
+ Hits         1863     1880      +17     
- Misses        147      151       +4     

Impacted Files	Coverage Δ
src/mp_api/routes/_general_store/client.py	0.00% <0.00%> (ø)
src/mp_api/routes/_general_store/query_operator.py	100.00% <100.00%> (ø)
src/mp_api/routes/electrodes/client.py	87.50% <0.00%> (-4.17%)	⬇️

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