feat(#3936): Add 'post-comment' Workflow

[volodya-lombrozo]

I added a simple workflow that runs on the master branch. Since it uses workflow_run event and runs on the master branch, GITHUB_TOKEN has read and write permissions.
This allow it to post comments to PRs.
Actually, we have only two steps here:

• Download the message for printing.
• Post this message to a PR.

By adding this workflow, we can provide benchmarking in a more secure environment without requiring write permissions.

Related to #3936

[volodya-lombrozo]

@yegor256 What do you think?

[yegor256]

@volodya-lombrozo let's try

[github-actions]

🚀 Performance Analysis

Test	Base Score	PR Score	Change	% Change	Unit	Mode
benchmarks.XmirBench.xmirToEO	166.849	162.234	-4.615	-2.77%	ms/op	Average Time
benchmarks.XmirBench.xmirToPhi	178.674	141.625	-37.050	-20.74%	ms/op	Average Time
benchmarks.XmirBench.xmirToSaltyPhi	162.357	149.994	-12.363	-7.61%	ms/op	Average Time

✅ Performance gain: benchmarks.XmirBench.xmirToEO is faster by 4.615 ms/op (2.77%)
✅ Performance gain: benchmarks.XmirBench.xmirToPhi is faster by 37.050 ms/op (20.74%)
✅ Performance gain: benchmarks.XmirBench.xmirToSaltyPhi is faster by 12.363 ms/op (7.61%)

[yegor256]

@volodya-lombrozo looks nice!