[#70452106] Rename catalog and catalog_item

#### Deprecate catalog_item for vapp_template_name

The new name more clearly describes its purpose for people that don't have
existing knowledge of VMware vCloud Director.

Change all existing test configs. Make the new name take precedence over the
old. Add a test to demonstrate that the old name can still be used if
the new isn't specified. Schema validation from Vcloud::Core::ConfigLoader
will take care of logging warnings for us.

#### Deprecate catalog for catalog_name

The replacement makes it clear that this item expects a string of the
"friendly name" rather than e.g. a UUID. It also aligns more closely with
`vdc_name` and the new `vapp_template_name` from the previous commit.