[feat] Add option to install pygelf in boostrap script

[teojgo]

Fixes #1522

[codecov-io]

Codecov Report

Merging #1529 into master will increase coverage by 0.53%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1529      +/-   ##
==========================================
+ Coverage   87.37%   87.90%   +0.53%     
==========================================
  Files          43       43              
  Lines        6558     6848     +290     
==========================================
+ Hits         5730     6020     +290     
  Misses        828      828              

Impacted Files	Coverage Δ
reframe/utility/color.py	100.00% <0.00%> (ø)
reframe/core/containers.py	100.00% <0.00%> (ø)
reframe/frontend/cli.py	79.61% <0.00%> (+<0.01%)	⬆️
reframe/core/buildsystems.py	97.11% <0.00%> (+0.01%)	⬆️
reframe/utility/__init__.py	91.55% <0.00%> (+0.05%)	⬆️
reframe/core/decorators.py	96.90% <0.00%> (+0.06%)	⬆️
reframe/frontend/executors/__init__.py	98.69% <0.00%> (+0.09%)	⬆️
reframe/frontend/argparse.py	92.30% <0.00%> (+0.12%)	⬆️
reframe/core/config.py	90.82% <0.00%> (+0.13%)	⬆️
reframe/core/schedulers/local.py	95.83% <0.00%> (+0.18%)	⬆️
... and 17 more

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[vkarak]

lgtm