Let user change the job name of benchmarks

[mimischi]

Fixes #85

Changes made in this pull request:

• Added --job-name option to mdbenchmark generate.
• Added new variable {{ job_name }} to be rendered in job templates.
• Changed all MPCDF templates to include the new variable {{ job_name }}.

PR Checklist

• Added changelog fragment in ./changelog/ (more information)?
• Issue raised/referenced?

[codecov]

Codecov Report

Merging #125 into develop will increase coverage by 0.01%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop     #125      +/-   ##
===========================================
+ Coverage    96.11%   96.12%   +0.01%     
===========================================
  Files           14       14              
  Lines          720      723       +3     
===========================================
+ Hits           692      695       +3     
  Misses          28       28

Impacted Files	Coverage Δ
mdbenchmark/generate.py	100% <100%> (ø)	⬆️
mdbenchmark/mdengines/utils.py	100% <100%> (ø)	⬆️

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