[FLINK-37778][1/N] introduce MODEL keyword for model as argument

[lihaosky]

What is the purpose of the change

Parse MODEL keyword in function argument and convert it to SqlExplicitModelCall with SqlExplicitModelOperator.

Brief change log

• Parser changes to support MODEL keyword in function argument.
• SqlExplicitModelCall sql node for model argument
• SqlExplicitModelOperator sql operator

Verifying this change

Added unit test for parser changes

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): (yes)
• 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? (JavaDocs)

[flinkbot]

CI report:

• e174dcc Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build

[fsk119]

Thanks for your contribution. I just have one question.

[fsk119]

Do we need this? We can use SqlOperator#createCall to build the SqlCall.

[lihaosky]

I'm planning to use this to get and store the model based on functionQualifier later in SqlValidatorImpl. It won't be possible with just SqlBasicCall

[fsk119]

OK. I think we can discuss more implement details when validating sql node.