[web] Make AddMembersList more universal

Summary:
Depends on D5115
AddMembersList component could be reused in another modals (i.a. in next diff - ComposeSubchannelModal)

Main changes:

a) split AddMembersList to 2 components:

1. AddMembersListContent- contains logic responsible directly for data processing for Members modal
2. AddMembersList - generate list

b) create directory for common modal components (web/modals/components)

c) move all associated with current AddMembersList components to web/modals/components

Test Plan:

1. Open any chat on web and open Members modal
2. Click "Add members"

AddMemberList works as before

Reviewers: tomek, atul, rohan, ginsu

Reviewed By: tomek, atul

Subscribers: ashoat, tomek, atul, abosh

Differential Revision: https://phab.comm.dev/D5185