Add support to provide a custom upgrade path to a test version

[SrishT]

Description

Currently the bookkeeper operator provides support to install a test version which has not yet been released and is therefore not a part of the supported versions config map. However, there is no way today to supply a custom upgrade path in the supported versions configmap, which could allow testing out any upgrade paths including to non released versions.

Importance

This issue is not a blocker as there is a workaround to achieve this by editing the bk-supported-versions configmap. However it is something that we should definitely add support for.

Location

charts

Suggestions for an improvement

We could add two values under test mode, fromVersion and toVersion.