fix(schema): Make inventory JSON Schema match actually accepted inventories

[viccie30]

This matches what ansible.builtin.yaml accepts as input.
Working on this I have a few questions:

1. The all group had a groups property, but that doesn't seem to be accepted by Ansible, so I removed it. Is that correct?
2. vars and children also accept a string, like hosts, and turn this into a dictionary with the string as a key and null as the value. It does not seem really useful, but because the syntax is accepted I added it to the schema.
3. Host and group variables starting with a digit are accepted, but are deprecated. I've written the schema to reject them, is this the wanted behavior?

[viccie30]

I have no clue why the schemas test fails. I get the same error locally, but I have no idea what's wrong with my changes to make it fail like that.

[viccie30]

I have no clue why the schemas test fails. I get the same error locally, but I have no idea what's wrong with my changes to make it fail like that.

Found it: the examples property was abused to list filenames. I've changed it to x-ansible-lint.

The duplication of the error is because all is validated against both patternProperties and its specific entry under properties. The explicit duplication under properties is only to update the description for all and unbound, so it can be removed without further problems if preferred.