[FLINK-18526][python][docs] Add configuration of Python UDF to use Ma…

[shuiqiangchen]

What is the purpose of the change

Add the configuration of Python UDF using Managed Memory in the doc of Pyflink

Brief change log

• add configuration of Python UDF example code to use managed memory in python_udfs.md.
• add configuration of Python UDF example code to use managed memory in vectorized_python_udfs.md.

Verifying this change

This changed is a doc update that has need to have test voverage.

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/Mesos, ZooKeeper: (no)
• The S3 file system connector: (no)

Documentation

• Does this pull request introduce a new feature? (no)

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Automated Checks

Last check on commit cbd3259 (Wed Jul 08 12:37:19 UTC 2020)

Warnings:

• Documentation files were touched, but no .zh.md files: Update Chinese documentation or file Jira ticket.

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Review Progress

• ❓ 1. The [description] looks good.
• ❓ 2. There is [consensus] that the contribution should go into to Flink.
• ❓ 3. Needs [attention] from.
• ❓ 4. The change fits into the overall [architecture].
• ❓ 5. Overall code [quality] is good.

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CI report:

• 84411ab Azure: SUCCESS

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