feat(zebra-network): add user agent argument

[oxarbitrage]

Motivation

We want to give zebra-network the possibility of changing the user agent it will use and we also want Zebra to automatically build the user agent by using git data.

Close #2375

Solution

• From zebrad, build and pass valid user agent to network.
• Build the user agent too in zebra-rpc as it is needed in the getinfo rpc method. We have app_version data already here, was needed for the same getinfo function, so we have everything to build user agent there too.

Review

I think anyone can review, this reduce the number of steps from the release checklist.

Reviewer Checklist

• Will the PR name make sense to users?
  • Does it need extra CHANGELOG info? (new features, breaking changes, large changes)
• Are the PR labels correct?
• Does the code do what the ticket and PR says?
  • Does it change concurrent code, unsafe code, or consensus rules?
• How do you know it works? Does it have tests?

Follow Up Work

[teor2345]

I just want to say that I love deleting stuff from the release checklist 🎉

[codecov]

Codecov Report

Merging #6601 (44a38d1) into main (58bd898) will increase coverage by 0.09%.
The diff coverage is 71.05%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6601      +/-   ##
==========================================
+ Coverage   77.82%   77.92%   +0.09%     
==========================================
  Files         308      309       +1     
  Lines       40331    40653     +322     
==========================================
+ Hits        31386    31677     +291     
- Misses       8945     8976      +31     

[teor2345]

Just letting you know that PR #6606 changes the format of the git version string in some cases. I don't know if that will impact this PR.

If you'd like, you can add:

Depends-On: #6601

to the PR #6606 description, which will make my PR wait for this one to merge. Then if anything breaks I can fix it.

(Just so you know, I'm not planning on reviewing this PR, because Marek is assigned to it.)

[upbqdn]

Looks great. I left two optional suggestions and one question.

[oxarbitrage]

Thanks! I added your doc suggestions and i tried to reply the question.