Use events stream for all long-running operations [WD-6846]

[lorumic]

Done

• Removed all usages of watchOperation, to generalise the usage of the events stream for all long-running operations.

Fixes WD-6846

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 the following operations all work as expected, and that they notify success/failure correctly once completed:
     1. Delete cached image
     2. Instance bulk actions including bulk delete
     3. Project rename
     4. All snapshot operations: create, restore, delete, rename, update and bulk delete
     5. Custom ISO upload

[webteam-app]

Demo starting at https://lxd-ui-506.demos.haus

[edlerd]

Good work, test and code looks good.