Fix inventory source caching by separating the fetching of objects and
populating the inventory. This way objects can be fetched from the K8S
API or from a configured cached and the cache related parameters on the
plugin now actually work.
The inventory source cache was tested with the ansible.builtin.jsonfile
cache plugin and 100k hosts (~2G JSON file). Though it took a noticeable
amount of time for the inventory plugin to run it worked fine and no
failures could be observed.
Signed-off-by: Felix Matouschek <fmatouschek@redhat.com>
