[FLINK-36595][docs] Explicitly set connector compatibility as string …

[hlteoh37]

…to prevent version comparison mismatch

Purpose of the change

• Set version as string to prevent version comparison mismatch. Issue has happened for other connectors too : https://github.com/apache/flink-connector-kafka/pull/132

Significant changes

(Please check any boxes [x] if the answer is "yes". You can first publish the PR and check them afterwards, for convenience.)

• [ ] Dependencies have been added or upgraded
• [ ] Public API has been changed (Public API is any class annotated with @Public(Evolving))
• [ ] Serializers have been changed
• [ ] New feature has been introduced
  • If yes, how is this documented? (not applicable / docs / JavaDocs / not documented)

[boring-cyborg[bot]]

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[davidradl]

LGTM

CI is failing.