* Add auth support for gRPC

* Add comment on static headers

* Update examples/otlptrace/src/main/java/com/google/cloud/opentelemetry/example/otlptrace/OTLPTraceExample.java

Co-authored-by: David Ashpole <[email protected]>

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Co-authored-by: David Ashpole <[email protected]>

* Add initial setup files for new example

* Add functioning spring boot application

* add additional mappings to enhance sample

* Add spring boot application properties

* Update spring application to generate traces

* Run application in GKE

* Fix bug in credential refresh

* Add client application to test credential refresh

* Add readme for sample

* Add missing EOF lines

* Readme style update

* Change OTel quickstart to use log4j2 instead of logback

Log4j2's `JsonTemplateLayout` supports most of the Cloud Logging special JSON keys directly through the [`GcpLayout` event template](https://logging.apache.org/log4j/2.x/manual/json-template-layout.html#event-templates). I still needed to map the OTel MDC keys for trace correlation, but am planning to contribute [this upstream](https://github.com/apache/logging-log4j2/blob/rel/2.17.2/log4j-layout-template-json/src/main/resources/GcpLayout.json).

One outstanding issue is converting the `trace_flags` hex value to a boolean, but it doesn't break Cloud Console if `logging.googleapis.com/trace_sampled` key is unset/false. See apache/logging-log4j2#2482.

* undo one collector config change, add issue ID to TODO

otel.java.experimental.extesion JVM Flag was updated to
otel.java.extension since Release v1.30.0

* Fix #258 enable mapping when not gcp kubernetes

* fix code style

* added comment for posterity

* Added label's mappings each mr_type

* Update to JUnit5 and refactor with ParameterizedTest

* Update code style for test

* Fix code style

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Co-authored-by: Pranav Sharma <[email protected]>

* Fix handling of null platform values according to spec.

* Use appropriate cloud provider values in tests

* Adds missing test cases

* Fixed the order about test cases & added comments

* Add support for custom MR mappings

* Add missing Javadoc for MonitoredResourceMapping

* Add unit tests for custom MR mappings

* Update platform metric mapping logic and rename MonitoredResourceDescription

* fix values in unit test

* Add unit test for no labels

* refactor: convert to unmodifieable set in constructor

* Add unit test for empty resource attributes

* remove redundant reference to this

* update formatting; add missing Javadoc

* Add warning message for MR type mismatch

* Update label name in test to avoid confusion

* rename DEFAULT_MONITORED_RESOURCE_DESCRIPTION -> EMPTY_MONITORED_RESOURCE_DESCRIPTION

* Set MR labels only if found