Better error message when launching fails

**What are you trying to do?**
launch a vm to test changes for a pr related to sbuild docs on 24.04

**What's your proposed solution?**
I tried to run the following command to clearly differentiate between test environments.

```
$ multipass launch 24.04 --name sbuild-docs-24.04
launch failed: Invalid arguments supplied
Invalid instance name supplied: sbuild-docs-24.04
```

**Additional context**
The problem here is that the error message does not tell me what I need to do to make it work.

A great error message consists of three parts.

- What happened?
- Why did it happen?
- How do I fix it?

The current error message only covers the first part, and leaves the user in the dark about why exactly it failed and what a viable solution might be.

A better error message would be

```
Invalid instance name: 'sbuild-docs-24.04'

Instance names may contain only:
- letters
- numbers
- hyphens

Dots (.) are not allowed.

Try:
multipass launch 24.04 --name sbuild-docs-2404
```

Actually, I made this up... checking https://documentation.ubuntu.com/multipass/stable/reference/instance-name-format/ - it is even a bit more strict. We could even link to that document in case you do not want to include the whole description in the error message.

Reproduce the failure with `multipass launch 24.04 --name sbuild-docs-24.04`, then trace the instance-name validation used by the launch command. Use the instance-name-format documentation linked in the issue as the reference; done means the error explains the permitted format and a viable correction or documentation link.

Written by the indexing model from the issue text.