Warn when leaving the terminal and interacted with it

[lorumic]

Done

• Migrated the old BrowserRouter to the more modern createBrowserRouter - recommended practice, see docs here.
• Added a confirmation prompt that is displayed when navigating away from the terminal tab if the user has interacted with the terminal.

QA

1. Run the LXD-UI:
   • On the demo server via the link posted by @webteam-app below. This is only available for PRs created by collaborators of the repo. Ask @lorumic or @edlerd for access.
   • With a local copy of this branch, run as described here.
2. Perform the following QA steps:
   • Check that navigation, contexts and routes all work as expected after the migration
   • Go to instance list
   • Open the detail page of a running instance
   • Go to Terminal tab / Console tab
   • Interact with the terminal or the text console, e.g. by writing a command (or just a single letter)
   • Try navigating away, e.g. by clicking on the "Logs" tab
   • Check that a prompt appears asking you if you really want to leave the page
   • Check that the Cancel/OK buttons work as expected

[webteam-app]

Demo starting at https://lxd-ui-521.demos.haus

[edlerd]

LGTM