Fix Jaeger remote sampler declarative config polling interval key

[thswlsqls]

Fixes #8648

Description

• JaegerRemoteSamplerComponentProvider.create() read config.getLong("internal"), a key that does not exist, so getLong always returned null and the configured polling interval was silently dropped.
• The schema model ExperimentalJaegerRemoteSamplerModel defines the field as @JsonProperty("interval"), matching the sibling keys endpoint and initial_sampler that were already correct.
• Changed the key to "interval" so a user-configured value is honored; when omitted the builder default (60000ms) still applies.
• Regression from Add file configuration ComponentProvider support for samplers #6494.

Testing done

• Added SamplerFactoryTest#create_JaegerRemote_interval (configured 10000ms honored) and #create_JaegerRemote_intervalDefault (omitted → 60000ms default), driving the real declarative pipeline.
• Added a package-private pollingIntervalMs field and getPollingIntervalMs() visible-for-testing accessor on JaegerRemoteSampler so the interval can be observed; no public API change (apidiff unchanged).
• Confirmed the interval test fails on the un-fixed key (expected: 10000 but was: 60000) and passes after the fix.
• ./gradlew :sdk-extensions:jaeger-remote-sampler:check — passed.
• ./gradlew :sdk-extensions:declarative-config:check — passed (SamplerFactoryTest: 19 tests).

[opentelemetry-pr-dashboard]

Pull request dashboard status

Status last refreshed: 2026-07-21 04:24:24 UTC.

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[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 91.64%. Comparing base (09d6c17) to head (9bfdee7).

Files with missing lines	Patch %	Lines
...sion/trace/jaeger/sampler/JaegerRemoteSampler.java	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #8649   +/-   ##
=========================================
  Coverage     91.64%   91.64%           
- Complexity    10348    10349    +1     
=========================================
  Files          1013     1013           
  Lines         27380    27382    +2     
  Branches       3218     3218           
=========================================
+ Hits          25092    25095    +3     
  Misses         1558     1558           
+ Partials        730      729    -1     

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