Allow users to share searches

As a user, I want to easily share searches with my colleagues.

The search page URL's already update to reflect the current search, so users can share links. However these links are potentially long. This feature would generate shortlinks when sharing a search:

- Add a share button on the search pages
- When the user clicks the button, store the URL in firestore and generate a short URL referencing the saved search, then share the link with the user
- When opening a shortlink, look up the URL in firestore and push it onto the router

We could use this approach to share other links within the site as well