feat: use OpenTelemetry for traces, logs and metrics

[daniel-mader]

Description of change

Replaces the following PRs:

• feat: initialize axum instrumentation with OpenTelemetry #303
• feat: replace init-tracing-opentelemetry with opentelemetry-appender-tracing for OTel log export #307 (follow up to PR 303)
• feat: Introduce OpenTelemetry for logs, traces, and metrics #308 (Copilot)

The default OpenTelemetry SDK env variables are strictly followed.

Links to any relevant issues

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How the change has been tested

Describe the tests that you ran to verify your changes.
Make sure to provide instructions for the maintainer as well as any relevant configurations.

Definition of Done checklist

Add an x to the boxes that are relevant to your changes.

• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have successfully tested this change in a docker environment

[codecov-commenter]

Codecov Report

❌ Patch coverage is 29.59641% with 157 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
agent_application/src/telemetry.rs	0.00%	99 Missing ⚠️
agent_application/src/lib.rs	0.00%	33 Missing ⚠️
agent_application/src/credential_metrics.rs	74.32%	19 Missing ⚠️
agent_api_http/src/metrics.rs	0.00%	4 Missing ⚠️
agent_store/src/lib.rs	84.61%	2 Missing ⚠️

Files with missing lines	Coverage Δ
agent_shared/src/config/mod.rs	89.78% <ø> (ø)
agent_store/src/lib.rs	78.48% <84.61%> (+0.07%)	⬆️
agent_api_http/src/metrics.rs	0.00% <0.00%> (ø)
agent_application/src/credential_metrics.rs	74.32% <74.32%> (ø)
agent_application/src/lib.rs	0.00% <0.00%> (ø)
agent_application/src/telemetry.rs	0.00% <0.00%> (ø)

... and 2 files with indirect coverage changes

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