Update GROMACS expanded ensemble patches

[ptmerz]

Description

Update GROMACS expanded ensemble patches to include the new bias
query not updating the forces, and clarify the user interface.

Based on discussions with @GiovanniBussi, @mrshirts, @wehs7661.

Target release

I would like my code to appear in release v2.8, ideally.

Type of contribution

• changes to code or doc authored by PLUMED developers, or additions of code in the core or within the default modules
• changes to a module not authored by you
• new module contribution or edit of a module authored by you

Copyright

• I agree to transfer the copyright of the code I have written to the PLUMED developers or to the author of the code I am modifying.

Tests

• I added a new regtest or modified an existing regtest to validate my changes.
• I verified that all regtests are passed successfully on GitHub Actions.

[codecov-commenter]

Codecov Report

Merging #793 (3c5209d) into v2.8 (d28c8e1) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             v2.8     #793   +/-   ##
=======================================
  Coverage   85.79%   85.79%           
=======================================
  Files         595      595           
  Lines       48572    48572           
=======================================
  Hits        41672    41672           
  Misses       6900     6900           

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