Rename beyla_build_info for internal registry

[marctc]

When Beyla is configured to have same port and path for prometheus exporter and internal metrics
means that the same Prometheus registry. This causes a panic because it tries to register beyla_build_info.

I tried different approaches to avoid register duplicated metrics but all the implementations are quite hacky,
as there's not a proper way to see if a metric is already register.

The easiest approach is to rename beyla_build_info to beyla_internal_build_info. So far it would only break
the internal debug dashboard.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 82.00%. Comparing base (e98ffbf) to head (05ced0f).

Files with missing lines	Patch %	Lines
pkg/internal/imetrics/iprom.go	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1119      +/-   ##
==========================================
- Coverage   82.02%   82.00%   -0.02%     
==========================================
  Files         140      140              
  Lines       11521    11520       -1     
==========================================
- Hits         9450     9447       -3     
- Misses       1550     1551       +1     
- Partials      521      522       +1     

Flag	Coverage Δ
integration-test	57.71% <50.00%> (+0.16%)	⬆️
k8s-integration-test	59.24% <50.00%> (+0.10%)	⬆️
oats-test	37.05% <0.00%> (-0.02%)	⬇️
unittests	52.36% <0.00%> (-0.02%)	⬇️

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[grcevski]

LGTM!