Expose n_repeats as experiment variant

[michaelmckinsey1]

Description

• Enables setting up multiple trials of the same experiment, to run in different resource allocations.
• Requires Batching experiments together #858 to run in same allocation.

Adding/modifying core functionality, CI, or documentation:

• Update docs/benchpark-setup.rst and lib/benchpark/experiment.py

[michaelmckinsey1]

Ignore Dane

[pearce8]

@michaelmckinsey1 does #858 need to be merged first?

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.21%. Comparing base (21613ec) to head (7f83452).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff              @@
##           develop    #1035       +/-   ##
============================================
+ Coverage    50.21%   65.21%   +14.99%     
============================================
  Files           25       44       +19     
  Lines         1643     3162     +1519     
  Branches       239      239               
============================================
+ Hits           825     2062     +1237     
- Misses         769     1093      +324     
+ Partials        49        7       -42     

Files with missing lines	Coverage Δ
lib/benchpark/experiment.py	87.94% <100.00%> (+41.67%)	⬆️
lib/benchpark/test/caliper.py	97.43% <ø> (ø)
lib/benchpark/test/experiment.py	100.00% <ø> (ø)

... and 30 files with indirect coverage changes

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