refactor(site): generalize UserCell component (#484)

Summary:

This is a first step in porting over v1 AuditLog in a refactored/cleaned
up fashion. The existing `UserCell` component was generalized for re-use
across various tables (AuditLog, Users, Orgs).

Details:

- Move UserCell to `components/Table/Cells`
- Add tests and stories for UserCell


Impact:

This unblocks future work in list views like the audit log, user management
panel and organizations management panel.

Relations:

- This commit relates to https://github.com/coder/coder/issues/472, but does not finish it.
- This commit should not merge until after https://github.com/coder/coder/pull/465 and https://github.com/coder/coder/pull/483 because it's
based on them.

site/src/api/types.ts

@@ -59,3 +59,10 @@ export interface Workspace {
 export interface APIKeyResponse {
   key: string
 }
+
+export interface UserAgent {
+  readonly browser: string
+  readonly device: string
+  readonly ip_address: string
+  readonly os: string
+}