Fix getMangedChannel typo in ExtendedGrpcSenderConfig

[thswlsqls]

Description

• Rename the misspelled getter getMangedChannel() to getManagedChannel() on ExtendedGrpcSenderConfig, and update its sole caller UpstreamGrpcSenderProvider. The typo was introduced in Refactor http, grpc senders and promote to public API #7782.
• The interface is internal (exporter.internal.grpc), so this is not a public API change: no apidiff (japicmp excludes internal packages), no CHANGELOG.
• The two AutoValue impls (ImmutableGrpcSenderConfig in exporters:otlp:all and sdk-extensions:jaeger-remote-sampler) call the generated constructor positionally, so AutoValue regenerates the property under the corrected name with no source edit.

Testing done

• Trivial typo on an internal identifier; behavior unchanged, no test added.
• ./gradlew :exporters:common:check :exporters:sender:grpc-managed-channel:check — passed.
• ./gradlew :exporters:otlp:all:compileJava :sdk-extensions:jaeger-remote-sampler:compileJava — passed; both AutoValue impls compile against the renamed method.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.62%. Comparing base (6f6e146) to head (b999356).

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #8604   +/-   ##
=========================================
  Coverage     91.62%   91.62%           
  Complexity    10321    10321           
=========================================
  Files          1013     1013           
  Lines         27287    27287           
  Branches       3203     3203           
=========================================
  Hits          25001    25001           
  Misses         1559     1559           
  Partials        727      727           

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