Fix: Update Fluent Bit setup to use prebuilt Loki plugin [4.4.0]

[wso2-engineering-bot]

This PR was automatically generated by Claude AI.

• Issue: Docs Instruct Building Fluent Bit from Source, but Prebuilt Loki Plugin Available #1623
• Type: Documentation
• Summary: Updated Fluent Bit setup instructions to remove outdated build-from-source steps since recent versions include the Loki plugin by default
• Style Scope Verification: Verified Microsoft Style Guidelines have been applied ONLY to newly added content without modifying existing content style unless specifically requested.
• Verification: mkdocs build passed

[chanikag]

Cannot merge, as the given set of remaining instructions are not compatible with the this Fluent Bit version.