Allow defining extra resource labels in prometheus

[mariomac]

Enables BEYLA_PROMETHEUS_EXTRA_RESOURCE_ATTRIBUTES to provide a list of additional resource attributes to be added to the reported target_info metric, in Prometheus.

Due to internal limitations of the Prometheus API client, Beyla needs to know beforehand which attributes are exposed
for each metric. This would cause that some attributes that are discovered at runtime, during instrumentation, won't
be visible by default. For example, attributes defined on each application via Kubernetes annotations, or in the
target application's OTEL_RESOURCE_ATTRIBUTES environment variable.

For example, an application defining the OTEL_RESOURCE_ATTRIBUTES=deployment.environment=production as environment
variable, the target_info{deployment.environment="production"} attribute would be visible by default if the metrics
are exported via OpenTelemetry but not if they are exported via Prometheus.

To make deployment_environment visible in Prometheus, you need to add it to the extra_resource_attributes list.

[marctc]

LGTM!

[github-actions]

This PR must be merged before a backport PR will be created.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.96%. Comparing base (6e7397a) to head (6b9188c).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1742      +/-   ##
==========================================
+ Coverage   65.84%   66.96%   +1.12%     
==========================================
  Files         214      214              
  Lines       22225    22241      +16     
==========================================
+ Hits        14634    14894     +260     
+ Misses       6855     6609     -246     
- Partials      736      738       +2     

Flag	Coverage Δ
integration-test	54.17% <100.00%> (+0.04%)	⬆️
k8s-integration-test	54.04% <100.00%> (+0.13%)	⬆️
oats-test	34.83% <0.00%> (?)
unittests	43.85% <44.44%> (-0.03%)	⬇️

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[rafaelroquetto]

Gnarly!

[mariomac]

Merging due to some urgency from affected users. @grafsean feel free to suggest any correction to the docs and I'll address them in another PR before merging 2.0 backport.

[github-actions]

The backport to release-2.0 failed:

Validation Failed: "Could not resolve to a node with the global id of 'T_kwDOAG3Mbc4AssrW'."

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new branch
git switch --create backport-1742-to-release-2.0 origin/release-2.0
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x 7dbd6642d73037e08de54f4f44d2caf7731cdf68

When the conflicts are resolved, stage and commit the changes:

git add . && git cherry-pick --continue

If you have the GitHub CLI installed:

# Push the branch to GitHub:
git push --set-upstream origin backport-1742-to-release-2.0
# Create the PR body template
PR_BODY=$(gh pr view 1742 --json body --template 'Backport 7dbd6642d73037e08de54f4f44d2caf7731cdf68 from #1742{{ "\n\n---\n\n" }}{{ index . "body" }}')
# Create the PR on GitHub
echo "${PR_BODY}" | gh pr create --title '[release-2.0] Allow defining extra resource labels in prometheus' --body-file - --label 'type/docs' --label 'backport' --base release-2.0 --milestone release-2.0 --web

Or, if you don't have the GitHub CLI installed (we recommend you install it!):

# Push the branch to GitHub:
git push --set-upstream origin backport-1742-to-release-2.0

# Create a pull request where the `base` branch is `release-2.0` and the `compare`/`head` branch is `backport-1742-to-release-2.0`.

# Remove the local backport branch
git switch main
git branch -D backport-1742-to-release-2.0