[FLINK-34989][ci] Reduces number of concurrent jobs for nightly runs

[XComp]

What is the purpose of the change

See FLINK-34989 for further details

Brief change log

• Introduced composite step to extract the release branch dynamically
• Dynamically selects release branch for nightly build: We reduce the nightly builds to running only every three days for now to reduce load on the runners
• Sets max-parallelism for test profiles to 2 which will limit the utilized runners to 20 (each test profile having 10+1 runners)

Verifying this change

• Test run for nightly trigger using dynamic branch extraction: https://github.com/XComp/flink/actions/runs/8526370193/job/23355456067
• Test run for documentation build using dynamic branch extraction: https://github.com/XComp/flink/actions/runs/8526394004/job/23355587218

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

[flinkbot]

CI report:

• 9960cbc UNKNOWN
• 2d45e7e Azure: SUCCESS
• e074b1b UNKNOWN

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