[DOCS] Registering Gems to project, engine, or .o3de registry

[chanmosq]

Describe the issue briefly

You can register a Gem to a project, engine, or the .o3de registry, depending on your workflow set up. Currently, there are only docs on registering Gems to a project here. We need docs to address the following:

• When should I register a Gem to a project vs. an engine vs. the registry?
• What are the CLI commands for registering to an engine and registry? And which files does this affect? (For example, registering to the engine updates external_subdirectories in the engine.json file.
• Any intermediate steps before I can see the Gem in my project? (For example, enabling the Gem to the project.) Is the process different/same depending on where I register the Gem?

Which page(s) / section(s) are affected?

Either A or B.

A

• https://o3de.org/docs/user-guide/project-config/register-gems/

  • Update this page to mention that you can also register Gems to the engine or registry, with a link to the docs.

• A doc about registering Gems in general that addresses the questions in the description above.

  • Not sure what section should this page go in?

B

• https://o3de.org/docs/user-guide/project-config/register-gems/
  • Update this page's title from "Registering Gems to a Project" to "Registering Gems".
  • Add info about registering Gems using all three methods.

Does this work have an engineering dependency? What is it?

No. If you have questions about registering Gems, reach out to #general or #sig-build channels in the O3DE Discord.

[sptramer]

sig-networking has also raised concerns that their gem requires manual configuration as part of enabling it - this is already documented, but it might be worth discussing with them if they have plans to integrate into some kind of automation so that our general guidance will work for it.

[chanmosq]

This task will produce documentation that addresses the following questions in this discussion comment:

Can I develop Gems under my own project folder or do we have to register and code version them in the same location as other external public Gems?