Support configuring ScyllaDB and Manager version for e2e test with a flag

[tnozicka]

We need to set up early testing against ScyllaDB and Manager pre-release so we need to have this configurable when running scylla-operator-tests. These flags should override the default version defined in the repository.

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/lifecycle stale

[tnozicka]

/remove-lifecycle stale /triage accepted