use replicas field in helm to decide if EPP should run in HA mode

[nirrozenbaum]

What type of PR is this?
/kind cleanup

What this PR does / why we need it:
use a single field (replicas) in the helm chart to decide whether EPP should run in HA mode or not.
this change verifies replicas is still overridable, and also verifies helm cannot be used to set active active mode.
if one uses replicas with a value greater than 1, helm will set HA in active passive mode.

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

None

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: nirrozenbaum

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[nirrozenbaum]

cc: @ahg-g @kfswain @liu-cong

[liu-cong]

I like this, and this is also extensible when we also supports active-active HA mode (such as adding a new HAMode parameter).

[liu-cong]

/lgtm

/hold to give others time to take a look. If we get this in today, I highly suggest we add it to the patch release #1616

[kfswain]

I agree, this looks great! I think this aligns closely with the intent of: #1620 (comment) and create a more flexible config surface. Thanks Nir!

[nirrozenbaum]

/unhold