This commit adds a custom helm release storage driver that overcomes
limitations in the size of a single value that can be stored in etcd.

In order to remain backward-compatible and also make this storage
driver available, this commit also refactors the ActionConfigGetter
options so that a custom function can be provided to the
ActionConfigGetter that can create the desired storage driver.

This commit also separates the rest config mapping into two separate
options. One for interactions with the storage backend, and the other
for managing release content.

Signed-off-by: Joe Lanford <joe.lanford@gmail.com>