BUG-8618: record LeaderFrontendState time
In order to deal with IsolatedLeader state and transaction timeouts,
we need to maintain an accurate view of when we have seen the frontend
even if we are not accepting messages from it.
Add correspoding field and maintain it whenever we interact with
LeaderFrontend state. Also record last connect ticks for the same use.
Change-Id: I8e49037507fcd01470a03be8c0d611efca55dabf
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>
(cherry picked from commit
7633a2a50144dad7cf987b29959dc06509575c05)