add simple CLI for testing message sending

[rkm]

Proposed Changes

Summarise your proposed changes here, including any notes for reviewers.

Types of changes

What types of changes does your code introduce? Tick all that apply.

• Bugfix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that would cause existing functionality to not work as expected)
• Documentation-Only Update (if none of the other choices apply)
  • In this case, ensure that the message of the head commit from the source branch is prefixed with [skip ci]

Checklist

By opening this PR, I confirm that I have:

• Reviewed the contributing guidelines for this repository
• Ensured that the PR branch is in sync with the target branch (i.e. it is automatically merge-able)
• Updated any relevant API documentation
• Created or updated any tests if relevant
• Created a news file
  • NOTE: This must include any changes to any of the following files: default.yaml, any of the RabbitMQ server configurations, GlobalOptions.cs
• Listed myself in the CONTRIBUTORS file 🚀
• Requested a review by one of the repository maintainers

Issues

If relevant, tag any issues that are expected to be resolved with this PR. E.g.:

• Closes #<issue-number>
• ...

[codecov]

Codecov Report

Patch coverage: 14.28% and project coverage change: -0.14 ⚠️

Comparison is base (a0903dc) 67.94% compared to head (3de3ebe) 67.81%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1520      +/-   ##
==========================================
- Coverage   67.94%   67.81%   -0.14%     
==========================================
  Files         185      186       +1     
  Lines        6546     6553       +7     
==========================================
- Hits         4448     4444       -4     
- Misses       2098     2109      +11     

Impacted Files	Coverage Δ
...lications.ServiceTester/ServiceTesterCliOptions.cs	0.00% <0.00%> (ø)
...rc/common/Smi.Common/Messages/FatalErrorMessage.cs	0.00% <0.00%> (ø)
src/applications/Applications.SmiRunner/Program.cs	33.82% <50.00%> (+0.49%)	⬆️

... and 3 files with indirect coverage changes

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