[HUDI-3661] Flink async compaction is not thread safe when use watermark

[danny0405]

Change Logs

The process function output collector is not thread safe, when the async executor in the CompactionFunction and the mailbox executor invokes the collector#output concurrently, the output buffer may corrupt.

In this PR, we replace the CompactFunction with a new CompactOperator within which the watermark events are ignored intentionally. The mailbox executor would expect to not modify the collector output buffer anymore.

Impact

Fix the concurremcy conflicts.

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

none

Documentation Update

Describe any necessary documentation update if there is any new feature, config, or user-facing change

• 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:

• aa89d92 Azure: PENDING

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