The pure CSI driver configuration uses a token while the respective storage
offload backend uses a user/pass, like the rest of the backends.
Forcing the use of two sets of credentials is undesirable, we want to re-use
the credentials the CSI deployment exposed.

Success criteria:
- Read the token from a secret entry
- Initiate the pure client with that token instead of trying to obtain the toakn
with user/pass

Undecided:
Should we introduce a new secret entry STORAGE_TOKEN?
- clearer
- but needs more handling (what happens if this AND STORAGE_PASSWORD is set?)
Should we reuse STORAGE_PASSWORD as a token if STORAGE_USERNAME is empty?
- if yes then should not fail validation if STORAGE_USERNAME is empty