Split robots between `maintained` and `unmaintained` and refactor CI dry-run accordingly

[pattacini]

We realized how a bunch of robots are incredibly old and they cost lots of effort to keep up to date (when this is still possible).

Thus, we decided to relegate them to a specific folder and keep them there until someone shows up, asking eventually for help.

Once done, the CI needs to be revised accordingly.

cc @maggia80 @Nicogene @traversaro

[pattacini]

My idea is to:

• Keep maintained robots at the root level so that no active forks will be impacted.
• Move other robots into the subdir unmaintained.
• Do all this after 2023.05.0 is released.

Also, the CI machinery should be modified to the least necessary (or even will stay unchanged), this way. With this process, I reckon we don't need to make an announcement as unmaintained robots are untouched for ages. At any rate, it holds what is said above:

until someone shows up, asking eventually for help.

cc @traversaro @Nicogene @maggia80

[pattacini]

Rather than unmaintained, I'd go for robots-icebox to point out that we will keep on providing support when partners possibly show up.

[pattacini]

PR:

• https://github.com/robotology/robots-configuration/pull/533