The restriction of the `apps._app_name_.command` property is too strict

I encountered this problem again with `command: bin/guvcview --audio=pulse` (the `=` character seems to be the trigger)

We are following the snapd restrictions now for command, I will add a snapd task to sort this.

I agree we want to lift this restriction.

I don't know when we'll find the time to do it (we need to make sure we're not using the fact it's restricted anywhere -- and we probably are).

Once snapd fixes the issue, snapcraft work can being to make sure we have end to end integration. Removing from the milestone until then.

It looks like the characters being requested here are probably:

- =
- "
- '
- {
- }

In addition, I filed 1827392 against snapd for = and :, so we would have the additional character of

- :

I encountered this bug again:

```output
+ snapcraftctl prime
The interpreter 'python3' for 'bin/git-filter-repo' was resolved to '/usr/bin/python3'.
The command 'bin/git-filter-repo' has been changed to '/usr/bin/python3 $SNAP/bin/git-filter-repo' to safely account for the interpreter.
Failed to generate snap metadata: The specified command '/usr/bin/python3 $SNAP/bin/git-filter-repo' defined in the app 'git-filter-repo' does not match the pattern expected by snapd.
The command must consist only of alphanumeric characters, spaces, and the following special characters: / . _ # : $ -
ubuntu #
```

However, this time I failed to see any invalid characters in the `/usr/bin/python3 $SNAP/bin/git-filter-repo` which only contains alpha-numerics, space, dollar sign, and slashes.

In the following build:

https://github.com/brlin-tw/snapcrafters-template-plus/actions/runs/3211397149/jobs/5249538457#step:3:1190

```
The interpreter 'bash' for 'bin/my-awesome-app' was resolved to '/bin/bash'.
The command 'bin/my-awesome-app' has been changed to '/bin/bash $SNAP/bin/my-awesome-app' to safely account for the interpreter.
Failed to generate snap metadata: The specified command '/bin/bash $SNAP/bin/my-awesome-app' defined in the app 'my-awesome-app' does not match the pattern expected by snapd.
The command must consist only of alphanumeric characters, spaces, and the following special characters: / . _ # : $ -
```

The command that triggers the error is "/bin/bash $SNAP/bin/my-awesome-app", which doesn't have any of the offending characters at all. There is a problem with the logic determining whether the command is acceptable.

Forgot to put on the source that renders the result:

Source: https://github.com/brlin-tw/snapcrafters-template-plus/tree/eff7426446cb7649460efa3c1beab8e70190d1ee