Simplify naming of toolbox images

[HarryMichal]

In the Dockerfiles of toolbox images we set the label name like this: name="$FGC/$NAME". That leads to the fact that the images are called in case of Fedora 31 like this: f31/fedora-toolbox. This naming schema is not right in my opinion. All these images are a fedora-toolbox with one difference and that is the version. But version should be handled by the version label.

I propose we change the naming to just: fedora-toolbox and use the label to manage versions. We could also start offering Rawhide as fedora-toolbox:rawhide.

[debarshiray]

This was fixed in #615

Until recently, the FGC namespace used to be required by the Fedora container guidelines.

[debarshiray]

I propose we change the naming to just: fedora-toolbox and
use the label to manage versions. We could also start offering
Rawhide as fedora-toolbox:rawhide.

At the least, we shouldn't refer to the images as rawhide, until the code knows how to interpret the string rawhide.

Beyond that, using rawhide to label the images might increase the amount of manual intervention that's necessary when a new Fedora release gets branched.