Add StartupProbe for Gitaly Pod

What does this MR do?

This MR lets the user enable and configure settings to add a startup probe to the Gitaly container. Startup probes are only used once during the initialization phase and runs before any other probes are run. If such a probe is configured, liveness and readiness probes do not start until it succeeds, making sure those probes don't interfere with the application startup. They differ from readiness probes as readiness probes continuously checks whether the container is ready to serve traffic throughout its lifecycle.

Ref: https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-startup-probes/

Related issues

Relates to gitlab-org/gitaly#6124

Author checklist

For general guidance, please follow our Contributing guide.

Required

For anything in this list which will not be completed, please provide a reason in the MR discussion.

• Merge Request Title and Description are up to date, accurate, and descriptive.
• MR targeting the appropriate branch.
• MR has a green pipeline.
• Documentation created/updated.
• Tests added/updated, and test plan for scenarios not covered by automated tests.
• Equivalent MR/issue for omnibus-gitlab opened.

Reviewers checklist

• MR has a green pipeline on https://gitlab.com/gitlab-org/charts/gitlab.
• Consider downstream impact to the Operator, as per evaluating impact from changes to GitLab Chart.