feat: add support for enterprise and child organizations

[jakedipity]

This begins support for terraform management of enterprise and child organizations:

• Allows the provider to accept an enterprise key to indicate an enterprise organization.
• Enterprise organizations can attach and detach child organizations.

Ref: LOG-13116 Signed-off-by: Jacob Hull jacob@planethull.com

[jsumners]

@jakedipity Mezmo laid me off on January 19. Please request a review from someone else.

[gjanco]

@jakedipity , you could add @seeruyy

[jakedipity]

Yeah sorry, that was a misclick on my part.