[fix][python client] Fixed reserved keys is not removed when JsonSchema being encoded

[boatrainlsz]

Fixes #15844

Motivation

JsonSchema doesn't remove reserved keys(_default,_required,_required_default) when being encoded. Resulting in confusing encoding output.

Modifications

Extract a common method to remove reserved keys when JsonSchema is being encoded, and this common method will be called when JsonSchema::encode method is called.

Verifying this change

• Make sure that the change passes the CI checks.

This change added tests and can be verified as follows:

• Added a unit test method named test_json_schema_encode_remove_reserved_key, see pulsar-client-cpp/python/schema_test.py

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

If yes was chosen, please highlight the changes

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API: (yes / no)
• The schema: (yes / no / don't know)
• The default values of configurations: (yes / no)
• The wire protocol: (yes / no)
• The rest endpoints: (yes / no)
• The admin cli options: (yes / no)
• Anything that affects deployment: (yes / no / don't know)

Documentation

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• doc-not-needed
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[github-actions]

@boatrainlsz:Thanks for your contribution. For this PR, do we need to update docs?
(The PR template contains info about doc, which helps others know more about the changes. Can you provide doc-related info in this and future PR descriptions? Thanks)

[merlimat]

The change looks good. Please remove the unintended changes to the config files.

[boatrainlsz]

The change looks good. Please remove the unintended changes to the config files.

Sorry for that, I will remove those unintended changes later

[boatrainlsz]

The change looks good. Please remove the unintended changes to the config files.

Sorry for that, I will remove those unintended changes later

@merlimat I've removed those changes, please kindly review it.

[boatrainlsz]

/pulsarbot run-failure-checks