chore: Externalise intialDelay & period of liveliness probe

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Description

Externalise initialDelaySeconds and periodSeconds of liveliness probe.

Motivation and Context

When the video PVC contains a lot of data, hub pod startup seems to take longer. The issue seems to happen when using AWS EFS for PVC, perhaps due to relatively slow IO on EFS. Increasing the initialDelaySeconds helps.

How Has This Been Tested?

Tested this in a cluster where the default initialDelaySeconds wasn't enough and using a higher value gave more time for hub pod to start.

Types of changes

[x] Bug fix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

[x] My code follows the code style of this project.
[x] My change requires a change to the documentation.
[x] I have updated the documentation accordingly.
[x] I have read the CONTRIBUTING document.
[ ] I have added tests to cover my changes.
[x] All new and existing tests passed.

zalando / zalenium