Bump required Elasticsearch to 7.*

[OskarPersson]

No description provided.

[codecov]

Codecov Report

Merging #935 into master will increase coverage by 0.00%.
The diff coverage is 28.57%.

@@           Coverage Diff           @@
##           master     #935   +/-   ##
=======================================
  Coverage   63.70%   63.70%           
=======================================
  Files         212      212           
  Lines       20392    20390    -2     
  Branches     2462     2462           
=======================================
- Hits        12991    12990    -1     
+ Misses       6953     6952    -1     
  Partials      448      448           

Flag	Coverage Δ
#backend	63.70% <28.57%> (+<0.01%)	⬆️

Impacted Files	Coverage Δ
ESSArch_Core/ip/views.py	57.40% <0.00%> (ø)
ESSArch_Core/search/alias_migration.py	46.66% <0.00%> (-0.21%)	⬇️
ESSArch_Core/tags/search.py	41.74% <50.00%> (ø)
ESSArch_Core/search/documents.py	76.19% <100.00%> (ø)

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