Add custom User-Agent to Hermes queries

[freak12techno]

Closes: #3979

Description

Adding custom User-Agent for all queries done via HttpClient (except for tests) by building HttpClient and providing it with a User-Agent header.

Here's now what's happening in Nginx logs on my node when I do hermes health-check:

<IP> - - [03/Jun/2024:15:50:48 +0200] "POST / HTTP/1.1" 200 1144 "-" "hermes/1.8.3"
<IP> - - [03/Jun/2024:15:50:49 +0200] "POST / HTTP/1.1" 200 73 "-" "hermes/1.8.3"
<IP> - - [03/Jun/2024:15:50:49 +0200] "POST / HTTP/1.1" 200 1144 "-" "hermes/1.8.3"
<IP> - - [03/Jun/2024:15:50:49 +0200] "POST / HTTP/1.1" 200 1144 "-" "hermes/1.8.3"
<IP> - - [03/Jun/2024:15:50:49 +0200] "POST / HTTP/1.1" 200 324 "-" "hermes/1.8.3"
<IP> - - [03/Jun/2024:15:50:50 +0200] "POST / HTTP/1.1" 200 6961678 "-" "hermes/1.8.3"

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PR author checklist:

• Added changelog entry, using unclog.
• Added tests: integration (for Hermes) or unit/mock tests (for modules).
• Linked to GitHub issue.
• Updated code comments and documentation (e.g., docs/).
• Tagged one reviewer who will be the one responsible for shepherding this PR.

Reviewer checklist:

• Reviewed Files changed in the GitHub PR explorer.
• Manually tested (in case integration/unit/mock tests are absent).

[freak12techno]

@romac can you look at that?

[romac]

Thanks!