add Resource getter to ExtendedOpenTelemetrySdk

[zeitlinger]

needed for https://github.com/open-telemetry/opentelemetry-java-contrib/pull/2296#discussion_r2515040501

[codecov[bot]]

Codecov Report

:x: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review. :white_check_mark: Project coverage is 90.11%. Comparing base (c67641c) to head (04521dd).

Files with missing lines	Patch %	Lines
.../extension/incubator/ExtendedOpenTelemetrySdk.java	66.66%	1 Missing :warning:

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #7832      +/-   ##
============================================
- Coverage     90.11%   90.11%   -0.01%     
  Complexity     7224     7224              
============================================
  Files           821      821              
  Lines         21809    21811       +2     
  Branches       2136     2136              
============================================
+ Hits          19654    19655       +1     
- Misses         1486     1487       +1     
  Partials        669      669              

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[zeitlinger]

@jack-berg wdyt?

[jack-berg]

Oof I want this but..

1. Even with breaking changes allowed in ExtendedOpenTelemetry, they still cause churn and we don't want to offer a capability and later have to withdraw it.
2. In my mind ExtendedOpenTelemetry is the place we prototype new ideas, but the scope is still bound to concepts in the spec. To my knowledge the spec doesn't talk about this right now. Though I suspect that's changing with entities, and I want to make sure anything we do is aligned with whatever the current thinking is there. It doesn't have to perfectly embody the latest thinking, but it shouldn't be in tension with that.

[zeitlinger]

@jsuereth what do you think?

Is it in line with entities to expose the resource in the extended otel instance?