Add support in RD GA4K for multiple inventory configmap and remove default inventory configmap

MR: gitlab-org/cluster-integration/gitlab-agent!1015 (merged)

Description

As part of our spike in Spike: GA4K: Decrypt data sent by rails to agen... (#414420 - closed) , we realized we need to support sending multiple inventory configmaps from rails. This allows us to send multiple sets of resources at different frequencies from rails to agent and not forces us to send all resources everytime we want to update something.

It was also noted that the default inventory configmap is never being used and should be removed.

Acceptance Criteria

• Add support for multiple inventory configmap
• Remove default inventory configmap