Add support for storage engine migration

[johscheuer]

What would you like to be added/changed?

If a user wants to change the storage engine right now with the operator this will require a manual step to change the storage migration type, otherwise the operator will be blocked changing the storage engine:

ERROR: Storage engine type cannot be changed because storage_migration_type=disabled.\nType `configure perpetual_storage_wiggle=1 storage_migration_type=gradual' to enable gradual migration with the perpetual wiggle, or `configure storage_migration_type=aggressive' for aggressive migration.

We should expose the:

storage_migration_type={disabled|aggressive|gradual}
perpetual_storage_wiggle=<WIGGLE_SPEED>
perpetual_storage_wiggle_locality=<<LOCALITY_KEY>:<LOCALITY_VALUE>|0>

options in the operator.

Part of this is to implement: #1482