Allow transaction tracking to be disabled

Allow transaction tracking to be disabled

Ask-based protocol does not need tracking of transactions and
histories, as it is not retransmitting requests. It also does
not inform backend about purely-local aborted transactions
(read-write and read-only), which leads to transaction tracking
rangesets having holes where those IDs are used.

This adds the prerequisite handling of disabling from the leader
without adding the actual mechanics.

JIRA: CONTROLLER-1879
Change-Id: I133e7688b492336937f394f0f6c3f080a05a820f
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>
Signed-off-by: Tomas Cere <tomas.cere@pantheon.tech>