feat: Check otelcol logs in COS tests

[MichaelThamm]

Issue

Our tests do not have great coverage, e.g. only checking that catalogue apps are reachable. We need more coverage on internal workings of COS.

Solution

Since otelcol is the aggregator (all data flows through it) within the COS model, it can indicate correct working operations. We can inspect this by checking the pebble logs. Check for:

• error
• warn

Checklist

• I have added or updated relevant documentation.
• PR title makes an appropriate release note and follows conventional commits syntax.
• Merge target is the correct branch, and relevant tandem backport PRs opened.

Context

Testing Instructions

Upgrade Notes