fix: add missing beforeDocumentControls custom component key for globals to importmap generation

[GeorgS]

What?

Add missing beforeDocumentControls key for custom components in admin.components.elements in globals to importmap generation. Remove editMenuItems from globals custom component docs.

Why?

Adding the custom components does currently not work as stated in the docs (https://payloadcms.com/docs/custom-components/edit-view#globals) as it won't be picked up by payload generate:importmap.

How?

Added missing key to generation. Update docs.

[AlessioGr]

@GeorgS build is failing

[GeorgS]

@AlessioGr did not realize that editMenuItems is currently not supported for Globals. I've removed it from the importmap generation and updated the docs to reflect the available custom components for Globals.