Add optional pre-upgrade hook delay

[mouchar]

Description of the change

Add optional delay before contacting etcd members in pre-upgrade helm hook checks.

Benefits

More reliable pre-upgrade hook, particularly on kubernetes clusters with slow network initialization. I observed delays between "pod started" and "network ready" events about 600ms, so simply setting this new variable to "1" should be enough in most cases.

Possible drawbacks

None, change is no-op if the variable is not set. If the variable is set, it slows down the helm hook run time by specified number of seconds.

Applicable issues

• fixes #82322