Adding missing tests for c8y-log-manager and fixing a bug that causes mqtt actor termination

[Ruadhri17]

Proposed changes

This PR consists of two parts:

1. Adding missing Robot framework tests for c8y-log-plugin.
2. Fixing bug in log manager: It returns error message instead of Ok(()) which cause mqtt actor termination

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (general improvements like code refactoring that doesn't explicitly fix a bug or add any new functionality)
• Documentation Update (if none of the other choices apply)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Paste Link to the issue

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA (in all commits with git commit -s)
• I ran cargo fmt as mentioned in CODING_GUIDELINES
• I used cargo clippy as mentioned in CODING_GUIDELINES
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

[didier-wenzek]

I confirm that the fix preventing the log-manager to abort on errors is correct.

[codecov]

Codecov Report

Merging #2161 (8b8961e) into main (4ea00b6) will decrease coverage by 0.1%.
The diff coverage is 0.0%.

Additional details and impacted files

Files Changed	Coverage Δ
crates/extensions/c8y_log_manager/src/actor.rs	80.6% <0.0%> (-0.2%)	⬇️

... and 2 files with indirect coverage changes

[github-actions]

Robot Results

✅ Passed	❌ Failed	⏭️ Skipped	Total	Pass %
253	0	5	253	100

[gligorisaev]

Checked and it looks ok

[didier-wenzek]

Approved