Workbench: upgrade to react-bootstrap 2 and Bootstrap 5

[emilyanndavis]

To keep the Workbench up to date with the latest bugfixes and security patches, we should upgrade react-bootstrap, and its Bootstrap dependency, to their current major versions.

Since Bootstrap 5 was a major rewrite compared to Bootstrap 4, there will be breaking changes. We should expect all or nearly all of our React components to be affected, and we will need to make several updates to the code.

We should follow the migration guides:

• React-bootstrap: Migrating to v2
• Bootstrap: Migrating to v5

... and be sure to perform thorough manual testing of the UI to minimize side effects.

Ideally, this work should be planned while we're not making UI-related updates, to avoid conflicts and re-work.