app: remove beacon node peer_id metric

[DiogoSantoss]

Remove previously added app_beacon_node_peer_id and move beacon node ID value to already existing metric beaconNodeVersionGauge.

category: feature
ticket: #4197

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 0% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.65%. Comparing base (f9042d5) to head (eca261a).
⚠️ Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
app/monitoringapi.go	0.00%	22 Missing ⚠️
app/app.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4264      +/-   ##
==========================================
- Coverage   56.91%   56.65%   -0.27%     
==========================================
  Files         237      237              
  Lines       31004    31329     +325     
==========================================
+ Hits        17646    17748     +102     
- Misses      11108    11308     +200     
- Partials     2250     2273      +23     

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