Documenting `customizations` and namespace contribution process

[bamurtaugh]

We have some info about contributing a new namespace and properties for a tool here, but it's not very detailed.

• When should a tool/org/company propose a new namespace?
• What does the contribution process look like (i.e. different detailed steps for publicly vs privately contributed namespaces)?

[avidal]

Agreed. I think it makes sense to adjust the docs so that customization namespaces reflect an organization identifier, similar to how the devcontainer/images repo labels images using the namespace dev.containers.*.

At Datadog, we're working on a devcontainers platform implementation and will likely have our own customization namespace (although it's unlikely to be "registered"), and will probably use com.datadoghq.<tool name>.

[Chuxel]

@avidal Yeah, adding a reverse DNS name under customizations is a safe way to avoid naming conflicts. Love to hear what you are looking into as well!