[web] introduce keyserver pill component

Summary:
This UI element will be repeated in several places in the keyserver selection list ui. Rather than copy + paste this logic a bunch of times, we should factor out this into a seperate + reusable component.

This is mainly a move diff; however, I did update the color variable names to follow our new color design system + made one change to the spacing between the two elements which I left a comment inline explaining

Test Plan:
Confirmed that there were no regressions with the create community modal

Reviewers: inka, michal, rohan

Reviewed By: inka

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D9905