Add LastCurrentTime to version info to tell if it ever became current (#692)

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SDK teams before merging! This is why the number of required approvals
is "2" and not "1"--two reviewers from the same team is NOT sufficient.
If your PR is not approved by someone in BOTH teams, it may be summarily
reverted._

<!-- Describe what has changed in this PR -->
**What changed?**
Add LastCurrentTime to version info to tell if it ever became current

<!-- Tell your future self why have you made these changes -->
**Why?**
So that the controller can accelerate rollout if it detects that the
target version was previously Current (aka it's actually a roll back)

<!-- Are there any breaking changes on binary or code level? -->
**Breaking changes**
None

<!-- If this breaks the Server, please provide the Server PR to merge
right after this PR was merged. -->
Doesn't break server, but here's the server PR:
temporalio/temporal#8845

Author: carlydf