Ensure volatile keys are preserved, when saving a network

[edlerd]

Done

• Ensure volatile keys are preserved, when saving a network

Fixes canonical/lxd#14531

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 @mas-who or @edlerd for access.
   • With a local copy of this branch, build and run as described in the docs.
2. Perform the following QA steps:
   • edit a network, that has settings under config.volatile.*
   • modify the network in the UI, ensure the save call contains all config.volatile keys in the payload

[webteam-app]

Demo

Jenkins

demos.haus