[FLINK-30558][runtime] Use different metric object to avoid metric 'numRestarts' being overridden by 'fullRestarts' in SchedulerBase

[SinBex]

What is the purpose of the change

Fix metric override each other. The method SchedulerBase#registerJobMetrics register metrics 'numRestarts' and 'fullRestarts' with the same metric object, which will result in the loss of the metric 'numRestarts'.

Brief change log

avoid metric 'numRestarts' being overridden by 'fullRestarts'

Verifying this change

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? (no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

[flinkbot]

CI report:

• 62d5014 Azure: SUCCESS

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[zhuzhurk]

Thanks for creating this PR! @SinBex
LGTM.