Introduce new option to generate statistics from multiple TF runs

[pholica]

Is your feature request related to a problem? Please describe.
N/A

Describe the solution you'd like
I have multiple TF runs (started by tesar) based on the very same request. TF provides different sets of results (e.g. due to infrastructure issues or unreliable tests). I'd like to see statistics (X passed Y failed Z errored of S executed) for each (corresponding) test plan and test.

Additional context
N/A

[github-actions]

Hi, there.

Thank you @pholica for suggesting this. Someone will take a look at this shortly.

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[pholica]

I've started working on this in https://github.com/pholica/tesar/tree/report_stats