Include cylc-flow & UIS version in sidebar

[MetRonnie]

Needs cylc-uis master (https://github.com/cylc/cylc-uiserver/pull/674)

Check List

• [x] I have read CONTRIBUTING.md and added my name as a Code Contributor.
• [x] Contains logically grouped changes (else tidy your branch by rebase).
• [x] Does not contain off-topic changes (use other PRs for other changes).
• [ ] Tests are included (or explain why tests are not needed).
• [ ] Changelog entry included if this is a change that can affect users
• [x] Docs not needed
• [x] If this is a bug fix, PR should be raised against the relevant ?.?.x branch.