[web] Introduce Label component

Summary:
Introduce a simple label component (for e.g. displaying member's role). It will be used in the next diff.

Figma:
https://www.figma.com/file/a1nkbWgbgjRlrOY9LVurTz/Comm-%2F-Desktop-app?node-id=1132%3A76670

Test Plan: No changes in the app. The component will appear in members modal.

Reviewers: palys-swm, benschac, atul

Reviewed By: palys-swm, atul

Subscribers: ashoat, palys-swm, Adrian, atul, karol-bisztyga, benschac

Differential Revision: https://phabricator.ashoat.com/D3378