[MINOR] Have BaseWriterCommitMessage implement Serializable

[CTTY]

Change Logs

Have BaseWriterCommitMessage implement Serializable. Recently we are exploring using Hudi with JavaSerializer instead of Kryo and found this minor gap. It shouldn't impact existing Hudi code.

Impact

None

Risk level (write none, low medium or high below)

none

Documentation Update

none

• The config description must be updated if new configs are added or the default value of the configs are changed
• Any new feature or user-facing change requires updating the Hudi website. Please create a Jira ticket, attach the
  ticket number here and follow the instruction to make
  changes to the website.

Contributor's checklist

• Read through contributor's guide
• Change Logs and Impact were stated clearly
• Adequate tests were added if applicable
• CI passed

[hudi-bot]

CI report:

• 7752e3f Azure: SUCCESS

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