## Problem
This is a narrow race that can leave a stuck Stopping tenant behind,
while emitting a log error "Missing InProgress marker during tenant
upsert, this is a bug"
- Deletion request 1 puts tenant into Stopping state, and fires off
background part of DeleteTenantFlow
- Deletion request 2 acquires a SlotGuard for the same tenant ID, leaves
a TenantSlot::InProgress in place while it checks if the tenant's state
is accept able.
- DeleteTenantFlow finishes, calls TenantsMap::remove, which removes the
InProgress marker.
- Deletion request 2 calls SlotGuard::revert, which upserts the old
value (the Tenant in Stopping state), and emits the telltale log
message.
Closes: #5936
## Summary of changes
- Add a regression test which uses pausable failpoints to reproduce this
scenario.
- TenantsMap::remove is only called by DeleteTenantFlow. Its behavior is
tweaked to express the different possible states, especially
`InProgress` which carriers a barrier.
- In DeleteTenantFlow, if we see such a barrier result from remove(),
wait for the barrier and then try removing again.
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Co-authored-by: Joonas Koivunen <joonas@neon.tech>
c48cc020bd