[FLINK-30284][flink-metrics] Adding datacenter url property to datadog

[rstpv]

What is the purpose of the change

This change deprecates the dataCenter configuration for DataDog reporter and replaces it with dataCenterUrl that allows users to configure whole address of the data center to use.

Brief change log

• Deprecates dataCenter key from DataDog reporter configuration (logs a warning to the users).
• Add new configuration option dataCenterUrl that accepts full address of Data Dog site, it defaults to US data center.

Verifying this change

Please make sure both new and modified tests in this PR follow the conventions for tests defined in our code quality guide.

This change is already covered by existing tests, such as DatadogHttpClientTest

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: (yes / no / don't know): no
• The runtime per-record code paths (performance sensitive): (yes / no / don't know): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (yes / no / don't know): no
• The S3 file system connector: (yes / no / don't know): no

Documentation

• Does this pull request introduce a new feature? (yes / no): yes
• If yes, how is the feature documented? docs

[flinkbot]

CI report:

• 9a14a7c212b387a58ba23f5ffde45d21a2c8a57c Azure: FAILURE

Bot commands

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[github-actions[bot]]

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