Add an e2e test for retryable NodeConfig mount units

[rzetelskik]

Description of your changes: It seems that the scenario described in #1559 has been covered by #2134. I wasn't able to find a scenario that would differentiate the case where a mount unit would require a restart to end up in an active state (as opposed to just starting it again as we do now), so this PR only adds an e2e covering the scenario described in the issue. We can go back to discussing the restarts if an actual scenario comes up.

Which issue is resolved by this Pull Request:
Resolves #1559

/kind feature
/priority important-longterm
/cc

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In response to this:

Description of your changes: wip

Which issue is resolved by this Pull Request:
Resolves #

/kind feature
/priority important-longterm
/cc

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[rzetelskik]

/cc zimnx tnozicka
ptal

[zimnx]

lgtm
/assign tnozicka

[rzetelskik]

ping @tnozicka

[tnozicka]

/approve

please
/hold
for #1955 (conflicts)

[scylla-operator-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: rzetelskik, tnozicka, zimnx

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