DEV: restore FT.AGG return info disclaimer

[dwdougherty]

@alonre24 Here's a PR for restoring the disclaimer to the return info for FT.AGG... . If the RESP3 information doesn't need a change, then this is all that's needed.

[github-actions]

Staging links:
https://redis.io/docs/staging/DOC-5869/commands/ft.aggregate/

[github-actions]

DOC-5869

[dwdougherty]

Thank you, @cmilesb!

[alonre24]

Thank you @dwdougherty !
Not completely related to this PR, but looking at FT.AGGREGATE docs under "Syntax": some of the optional keywords have a space before them, while others do not, which looks a bit strange. Is that intentional?
Also, the "## return value" header looks like it has a missing formatting

[dwdougherty]

Not intentional. Raz pointed this out to me a coupla days ago as well. I patched up the un-rendered heading and the syntax whitespace in the last commit. Thanks for catching those!