[FLINK-27661][flink-metrics-prometheus]PrometheusPushGatewayReporter support http basic auth

[littlecatjianjiao]

What is the purpose of the change

I found that the native PrometheusPushGatewayReporter cannot support pushgateway user authentication. However, our pushgateway just uses user authentication, so if the native reporter is used, the metrics data cannot be reported to the pushgateway.

Brief change log

• makes the PrometheusPushGatewayReporter support http basic auth(optional)

Verifying this change

Please make sure both new and modified tests in this PR follows the conventions defined in our code quality guide: https://flink.apache.org/contributing/code-style-and-quality-common.html#testing

(Please pick either of the following options)

This change is a trivial rework / code cleanup without any test coverage.

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: (no)
• The runtime per-record code paths (performance sensitive): (no)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (no)
• The S3 file system connector: (no)

Documentation

• Does this pull request introduce a new feature? (yes)
• If yes, how is the feature documented? (not documented)

[flinkbot]

CI report:

• d4e8e35 Azure: FAILURE

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