[feat][ws]Add support for initialSubscriptionPosition in Websocket Consumer

[moinessim]

Fixes #22969

Motivation

As a websocket client, I need to subscribe to a persistent topic that has existing messages.
I need to consume all messages, starting from the first (earliest) one, and keep consuming messages as they become available.
Persistent subscription cursor is needed, hence the use of consumer api.

There is no parameter available for this setting shown in the documentation, or in the code that creates the subscription.

There is a similar setting messageId for the Reader endpoint.
But not for the Consumer endpoint.

Modifications

Passthru the SubscriptionInitialPosition query parameter to the Consumer java API.

Verifying this change

• Make sure that the change passes the CI checks.

This change is a trivial rework / code cleanup without any test coverage.

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

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

• doc
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• doc-not-needed
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Matching PR in forked repository

PR in forked repository:

[lhotari]

[INFO] There are 2 errors reported by Checkstyle 10.14.2 with /home/runner/work/pulsar/pulsar/buildtools/src/main/resources/pulsar/checkstyle.xml ruleset.
Error:  src/main/java/org/apache/pulsar/websocket/ConsumerHandler.java:[436] (sizes) LineLength: Line is longer than 120 characters (found 140).
Error:  src/main/java/org/apache/pulsar/websocket/ConsumerHandler.java:[438] (sizes) LineLength: Line is longer than 120 characters (found 133).

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