[helm] Add k8s fields to pydantic schema
Summary: Adding more k8s fields to the pydantic schema, including InitContainers & VolumeMounts.
Test Plan: helm lint + bk
Reviewers: rexledesma, jordansanders
Reviewed By: rexledesma
Subscribers: johann
Differential Revision: https://dagster.phacility.com/D8439