Calls to with_resource for signal builders (Metrics, Logs, Traces) are now additive

[martintmk]

Fixes #2324

Changes

The calls to:

• MeterProviderBuilder::with_resource
• TracerProviderBuilder::with_resource
• LoggerProviderBuilder::with_resource

Are now additive and the previous resource is not discarded anymore. Additionally, I fixed a bug where setting the schema_url was discarded due to a bug how merging of resources was handled.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.2%. Comparing base (dc9a5c8) to head (374574c).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #2677     +/-   ##
=======================================
+ Coverage   79.1%   79.2%   +0.1%     
=======================================
  Files        122     122             
  Lines      22530   22621     +91     
=======================================
+ Hits       17839   17934     +95     
+ Misses      4691    4687      -4     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[cijothomas]

I agree with this change. Requesting changes to address below.

1. #2324 (comment) - Check this and see if this makes sense, given there are more than one ideas suggested in the linked issue.
2. Please make the change consistent across signals. (Okay to do that in separate PR to keep scope smaller)

[cijothomas]

@martintmk Edited the PR Desc slightly to mark the associated issue to be resolved with this PR.
Nice work, thanks for exploring and weighing all options and driving closure!
(I removed "breaking" wording from changelog.)