[doc] document disabling Stream Load compression via sink.properties.compress_type

[JNSimba]

Versions

• dev
• 4.x
• 3.x
• 2.1 or older (not covered by version/language sync gate)

Languages

• Chinese
• English
• Japanese candidate translation needed

Docs Checklist

• Checked by AI
• Test Cases Built
• Updated required version and language counterparts, or explained why not
• If only one language changed, confirmed whether source/translation counterparts need sync

Summary

Since Flink Doris Connector 26.1.0, gz compression is enabled by default for Stream Load (apache/doris-flink-connector#648). This PR documents how to disable it:

• Append to the 26.1.0 release note: compression can be disabled by setting 'sink.properties.compress_type' = ''.
• Append the same note to the sink.properties.* description in the connector configuration table so users can find it from the main config docs.

Applied to all four locations: docs/ (dev EN), versioned_docs/version-4.x/ (4.x EN), and the corresponding i18n/zh-CN Chinese translations.