[web] Create new chat button creates chat in GENESIS community only

Summary:
Changed create chat button when in non-GENESIS community to begin create channel experience.
Created onClickSubchannel which pushes ComposeSubchannelModal when communityID does not equal genesis.id.
Added conditional to change "Create new chat" to "Create new channel" when in non-GENESIS community.

Test Plan: Verified working on local web version and ran flow.

Reviewers: ashoat

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D9558