Add HumanWorker, OTTO Robots, RGL and UR Robots robotic Gems

[jhanca-robotecai]

Change summary

Multiple robotic Gems, external to o3de repositories, are missing from the documentation. I believe adding information about such Gems would narrow the learning curve of O3DE robotics.

The information about the following Gems was added:

• HumanWorker
• OTTO Robots
• RGL
• UR Robots

Note, that all Gems listed earlier are open source. Three of them were used in ROSCon2023Demo project, which received a significant audience during the conference and via online channels.

I also found several Gems in o3de-extras repository with missing documentation. These will be added in the following PR or the following commits.

Draft: the gems described in this PR will be officially released after o3de 2310.1 release.

Submission Checklist:

• [x] Descriptive active voice - Do descriptive sentences have a clear subject and action verb?
• [x] Answer the question at hand - Does the documentation answer a what, why, how, or where type of question?
• [x] Consistency - Does the content consistently follow the Style Guide?
• [x] Help the user - Does the documentation show the user something meaningful?

[adamdbrw]

I think this PR also includes (and very much expands on) the older one: https://github.com/o3de/o3de.org/pull/2504, which can be closed.