[improve] [admin] pulsar admin support get exact or whole batch message by id

[TakaHiR07]

Motivation

If we enable batch message, sometimes we need to get the exact message in a batch or get the whole batch messages to help find out some problems. But now the admin getMessageById() method can only get the first message in a batch.

Modifications

1. implement getBatchMessagesById() to get the whole batch messages in a entry
2. implement get the exact batch message in the getMessageById() methods, and ensure the compatibility with previous behaviour
3. add unittest for these implementation

Verifying this change

This change added tests and can be verified as follows:

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
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository: TakaHiR07#3

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