out_doris: doc for new doris out plugin

[joker-star-l]

Issue: fluent-bit/issues/9501 Code PR: fluent-bit/pull/9514

[joker-star-l]

Thanks for your contribution @joker-star-l! I suggested some changes from a technical writing perspective.

Thank you!

[eschabell]

@joker-star-l can you resolve the conflicts here, I also nudged you on the code PR https://github.com/fluent/fluent-bit/pull/9514.

[eschabell]

@patrick-stephens @lockewritesdocs the reviews are not showing approval yet, can one of you review the latest changes? Please do not merge yet after review, the code PR https://github.com/fluent/fluent-bit/pull/9514 needs to merge first.

[patrick-stephens]

We need to resolve conflicts before anything will be possible.

[joker-star-l]

We need to resolve conflicts before anything will be possible.

Yes. I will update the doc after the code pr is merged.