prod docs: Update BBB customization link.
prod docs: Update BBB customization link.

Updates the Big Blue Button link for customizing secrets
extraction.

eeshangarg/zulip,kou/zulip,andersk/zulip,kou/zulip,eeshangarg/zulip,eeshangarg/zulip,kou/zulip,zulip/zulip,zulip/zulip,rht/zulip,kou/zulip,andersk/zulip,eeshangarg/zulip,rht/zulip,zulip/zulip,zulip/zulip,rht/zulip,rht/zulip,andersk/zulip,eeshangarg/zulip,kou/zulip,rht/zulip,eeshangarg/zulip,zulip/zulip,andersk/zulip,eeshangarg/zulip,andersk/zulip,kou/zulip,andersk/zulip,rht/zulip,rht/zulip,zulip/zulip,andersk/zulip,kou/zulip,zulip/zulip