fix(instance): add name length check for instance name (creation/edit)

[lorumic]

Done

• Added length validation check for instance name (creation and edit)

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, run as described here.
2. Perform the following QA steps:
   • Create a new instance, input some text that is longer than 63 characters in the "Instance name" field, and check that a proper error message appears
   • Edit an existing instance, change the name in the header by inputting some text that is longer than 63 characters and check that a proper error message appears

[webteam-app]

Demo

Jenkins

demos.haus

[edlerd]

Thanks for improving the validation and making it reusable.