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

[nicusX]

Explicitly set connector compatibility as string 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

No significant change

[boring-cyborg[bot]]

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