Add spawning of remote controller (no local yaml file needed)

[mamueluth]

There are cases in which you want to spawn controllers running on a remote machine without the controllers.yaml beeing available on the local machine.
This PR extends the spawner with the option to activate a controller where the local .yaml file does not exist.

[codecov]

Codecov Report

❌ Patch coverage is 35.29412% with 33 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.73%. Comparing base (6d695b3) to head (e5ee815).
⚠️ Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
controller_manager/controller_manager/spawner.py	33.33%	19 Missing and 5 partials ⚠️
.../controller_manager/controller_manager_services.py	40.00%	6 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2349      +/-   ##
==========================================
- Coverage   88.90%   88.73%   -0.18%     
==========================================
  Files         148      148              
  Lines       16950    16993      +43     
  Branches     1448     1461      +13     
==========================================
+ Hits        15069    15078       +9     
- Misses       1318     1345      +27     
- Partials      563      570       +7     

Flag	Coverage Δ
unittests	88.73% <35.29%> (-0.18%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
.../controller_manager/controller_manager_services.py	78.73% <40.00%> (-3.80%)	⬇️
controller_manager/controller_manager/spawner.py	61.70% <33.33%> (-9.08%)	⬇️

... and 2 files with indirect coverage changes

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[bmagyar]

I think we really need some testing here. We should be able to run the same tests, they should just follow a different code path when we tell it it's a remote file, right?