Add default flank settings to optimize performance

[pawelpasterz]

Fixes #455

• Nexuslowres can make executions up to 4x faster due to smaller screen size.
• Disable video (results bucket significant smaller, skips processing time of generating video)
• Disable auto login (saves 30s - 1m)
• Disable performance metrics. (saves processing time)

Chnages

• Add FlankDefaults class to preserve defaults Flank settings
• Update unit tests
• Update documentation

Checklist

• Documented
• Unit tested

[codecov-io]

Codecov Report

Merging #644 into master will decrease coverage by 0.03%.
The diff coverage is 75%.

@@             Coverage Diff              @@
##             master     #644      +/-   ##
============================================
- Coverage     77.32%   77.29%   -0.04%     
  Complexity      613      613              
============================================
  Files            82       83       +1     
  Lines          2329     2330       +1     
  Branches        311      311              
============================================
  Hits           1801     1801              
- Misses          334      335       +1     
  Partials        194      194

[jan-goral]

I'm not sure if hiding default values behind constants was necessary. Any of those constant are used only once and they are not telling more than members which they are assigned. But we have one file more to check, if we want to know defaults.

[pawelpasterz]

In general case I agree. In this particular one I wanted to point explicitly that those are not default, gcloud values, and what those values mean (ex when I see DISABLE_VIDEO_RECORDING I would conclude that Flank's default setting is to have this disabled not being particularly interested if this is false, -1 or sth else). Probably enum based would be better but this will require bigger refactor that's why I decided to proceed with this solution.

I could also just change true -> false and leave additional comment why it is implemented that way.

TBH both solutions are fine for me. Let me know what you think, thanks!

[jan-goral]

That was only suggestion so you can leave it as is. Your arguments are reasonable, it's ok for me.