ENT-14444: Added cfengine test i2, now reports a test-suite using the assert-promise module

[SimonThalvorsen]

Runs test_*.cf files or a deployed policy's own assert: promises (or just a plain built-policy run) in disposable Docker container and reports a pytest-style pass/fail summary.
Adds --dockerfile/--rebuild flags for testing against a custom base image.

Ticket: ENT-14444

[codecov]

Codecov Report

❌ Patch coverage is 99.12281% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.41%. Comparing base (65afc1b) to head (079365b).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
...cfengine_cli/cfengine_wrapper/cfengine_commands.py	86.66%	2 Missing ⚠️
src/cfengine_cli/container.py	99.53%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #250      +/-   ##
==========================================
+ Coverage   55.16%   58.41%   +3.25%     
==========================================
  Files          33       34       +1     
  Lines        4164     4490     +326     
==========================================
+ Hits         2297     2623     +326     
  Misses       1867     1867              

Files with missing lines	Coverage Δ
src/cfengine_cli/commands.py	58.18% <100.00%> (-0.16%)	⬇️
src/cfengine_cli/main.py	61.50% <100.00%> (+0.48%)	⬆️
src/cfengine_cli/report.py	100.00% <100.00%> (ø)
src/cfengine_cli/container.py	99.55% <99.53%> (+10.08%)	⬆️
...cfengine_cli/cfengine_wrapper/cfengine_commands.py	32.52% <86.66%> (+2.57%)	⬆️

... and 1 file with indirect coverage changes

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