Should allow setting camera properties from `<gui><camera>`

[azeey]

Desired behavior

Currently, to set a camera property, e.g. it's pose, the user has to specify the MinimalScene plugin and set the value there. But this in turn disables all default plugins, so the user is forced to specify all the default plugins. It would be nice if the user can just set these properties in <gui><camera> and not have to specify any plugin.

Alternatives considered

none

Implementation suggestion

If the properties in <gui><camera> conflict with those manually set by the user in MinimalScene, the ones in <gui><camera> should be used.

[Ryanf55]

Is there any way to inherit GUI properties from a common sdf file? I am trying to reduce code duplication in my SDF's worlds, but every one of them needs a lot of duplicated <gui> even though they use similar layouts.