Fix intermittent issue on OciMetricsSupportTest

[klustria]

RCA is described here: #6112 (comment)

Changes include the following:

1. In OciMetricsSupportTest.testEndpoint, extend the amount of validation time to 10 seconds for checking that the metric endpoint has been restored. Intermittently, a race condition exist where the validation happens before the endpoint is restored.
2. Modify all countdownLatch to be locally defined in the test methods rather than being a static variable, which is causing chain reaction failure to other tests if a previous test fails because they share the same countdownLatch.
3. Always check that countDownLatch.await() is verified to have completed or otherwise, assert a failure.
4. Remove the use of fixed port when starting a WebServer.
5. Reset postingEndPoint to its original value before each test, so @RepeatedTest can be used in the future for debugging purposes.
6. Apply Helidon Code Style on both OciMetricsSupportTest and OciMetricsCdiExtensionTest. This would include making the tests's class and methods package local rather than public, rearranging variable fields order based on whether they are static, final, etc.
7. Note that OciMetricsCdiExtensionTest only involves Code Style change and removal of delay method which is never used, so logic in that test class will be the same as before. Only OciMetricsSupportTest contain significant change to resolve the issue reported.
8. Fail the OciMetricsCdiExtensionTest if enabled OCI Metrics validation times out on countDownLatch.await()