docs: Update GSoC ideas list.
docs: Update GSoC ideas list.

This list is by no means final, but it has substantial updates from
last year's list.

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