[FLINK-34745] Improve validations for a period in Time Travel

[dawidwys]

What is the purpose of the change

The provided SQLs are invalid, however the current code base fails on unexpected locations giving unhelpful messages. This PR improves the validation which results in proper error messages.

Verifying this change

Added tests.

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

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

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

[flinkbot]

CI report:

• 25d7256 Azure: SUCCESS

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[snuyanzin]

thanks for addressing comment
i have another nit one