settings: Improve check for incomplete org profile.
settings: Improve check for incomplete org profile.

Use a regex to check for the pattern "Organization
imported from ..." instead of the previous approach
where we just checked if pattern startswith "Organiztion
imported from".

This allows users to extend the description from the original
"Organization imported from Slack." with a few extra sentences without
this warning remaining indefinitely.

Fixes #17463

zulip/zulip,punchagan/zulip,hackerkid/zulip,rht/zulip,andersk/zulip,hackerkid/zulip,punchagan/zulip,punchagan/zulip,kou/zulip,rht/zulip,andersk/zulip,kou/zulip,eeshangarg/zulip,zulip/zulip,andersk/zulip,rht/zulip,kou/zulip,hackerkid/zulip,hackerkid/zulip,punchagan/zulip,punchagan/zulip,hackerkid/zulip,kou/zulip,zulip/zulip,kou/zulip,andersk/zulip,andersk/zulip,andersk/zulip,rht/zulip,zulip/zulip,hackerkid/zulip,zulip/zulip,eeshangarg/zulip,zulip/zulip,rht/zulip,eeshangarg/zulip,punchagan/zulip,kou/zulip,andersk/zulip,eeshangarg/zulip,kou/zulip,eeshangarg/zulip,eeshangarg/zulip,hackerkid/zulip,eeshangarg/zulip,rht/zulip,zulip/zulip,rht/zulip,punchagan/zulip