docs: Add docs for module creation (SC-961)

[TheRealFalcon]

Proposed Commit Message

docs: Add docs for module creation

Additionally remove the cc_foo module as any relevant documentation
there has been moved to the official documentation.

[holmanb]

I think this does a good job of covering what goes in the config module directory. Think we should add context for boot stage determination / cloud.cfg.tmpl / etc?

[blackboxsw]

Suggested change

	* ``examples``: Lists examples to be shown in the documentation.
	* ``examples``: Lists examples of any new cloud-config keys this module reacts to.
	These examples will be rendered in the module reference documentation.

[blackboxsw]

might want to express this as something a bit different from cc_example so it doesn't imply some sort of requirement to match the current module name.

Suggested change

	"cc_example: example1",
	"some_new_config_key: allowed_value",

[TheRealFalcon]

Addressed comments in a separate commit. Force push is only for rebase.

[blackboxsw]

Suggested change

	In order for a module to be run, it must be defined in ``/etc/cloud`` on the
	launched instance. The three module sections are
	In order for a module to be run, it must be defined in a module run section in
	``/etc/cloud/cloud.cfg`` or ``/etc/cloud/cloud.cfg.d`` on the launched instance.
	The three module sections are

[blackboxsw]

Minor thought on being clear about where the config files exist for changing such a value. If we don't point to /etc/cloud/cloud.cfg specifically, someone may inadvertently add a cloud_init_modules: [cc_my_mod] which would drop all of our predefined modules in the base config.

I'll defer to whether or not you think the specific comment is useful or needed but +1 regardless of your choice there in wording.

[holmanb]

Thanks for the cloud.cfg.tmpl addition. LGTM