Adds values.yaml fields for user-deployment liveness and startup probe.

Summary:
Intended to resolve GitHub issue #3305.

Previously, the liveness and startup probe for user-deployment pods was not exposed in the Dagster helm chart's values.yaml.

The defaults used were:

livenessProbe:
  # ...
  periodSeconds: 20
  timeoutSeconds: 3

startupProbe:
  # ...
  periodSeconds: 10
  timeoutSeconds: 3

This diff will keep these defaults, but expose them through the values.yaml. The following fields are now also exposed:

initialDelaySeconds
successThreshold
failureThreshold

Test Plan:
integration
bk

Run helm install on GCP elementl-dev cluster, check that pods and services are all helathy, and check that livenessProbe and startupProbe config is passed correctly (via kubectl describe pod).

Reviewers: catherinewu

Reviewed By: catherinewu

Subscribers: catherinewu, rexledesma

Differential Revision: https://dagster.phacility.com/D5476