docs: Clarify documentation on Amazon RDS.
docs: Clarify documentation on Amazon RDS.

It's not actually a reasonable experience to use Zulip without working
full-text search, so we should more strongly direct folks to not do
it.

Fixes #12724.

kou/zulip,zulip/zulip,kou/zulip,eeshangarg/zulip,tommyip/zulip,rishig/zulip,synicalsyntax/zulip,andersk/zulip,rht/zulip,andersk/zulip,punchagan/zulip,timabbott/zulip,rht/zulip,eeshangarg/zulip,hackerkid/zulip,zulip/zulip,zulip/zulip,shubhamdhama/zulip,tommyip/zulip,showell/zulip,eeshangarg/zulip,hackerkid/zulip,synicalsyntax/zulip,eeshangarg/zulip,andersk/zulip,zulip/zulip,eeshangarg/zulip,tommyip/zulip,zulip/zulip,brainwane/zulip,synicalsyntax/zulip,brainwane/zulip,rht/zulip,synicalsyntax/zulip,eeshangarg/zulip,shubhamdhama/zulip,eeshangarg/zulip,hackerkid/zulip,brainwane/zulip,timabbott/zulip,brainwane/zulip,synicalsyntax/zulip,kou/zulip,shubhamdhama/zulip,timabbott/zulip,showell/zulip,timabbott/zulip,kou/zulip,showell/zulip,kou/zulip,tommyip/zulip,hackerkid/zulip,rht/zulip,punchagan/zulip,rishig/zulip,showell/zulip,rishig/zulip,timabbott/zulip,showell/zulip,showell/zulip,synicalsyntax/zulip,timabbott/zulip,punchagan/zulip,shubhamdhama/zulip,shubhamdhama/zulip,tommyip/zulip,zulip/zulip,kou/zulip,synicalsyntax/zulip,kou/zulip,hackerkid/zulip,andersk/zulip,showell/zulip,brainwane/zulip,punchagan/zulip,rht/zulip,zulip/zulip,punchagan/zulip,brainwane/zulip,rishig/zulip,andersk/zulip,rht/zulip,andersk/zulip,hackerkid/zulip,punchagan/zulip,rishig/zulip,andersk/zulip,tommyip/zulip,brainwane/zulip,hackerkid/zulip,timabbott/zulip,punchagan/zulip,shubhamdhama/zulip,shubhamdhama/zulip,rishig/zulip,rishig/zulip,tommyip/zulip,rht/zulip