…actor-resthandler-state-machine-into-coro

- Temporarily disabled LogContext (ScopedValue in rest handler state
  machine)
- Made more stuff async
- Fixed an issue by moving a coro from Future to async, because futures
  don't pass ExecContext as coros (just as an awaitable)
- Fixed an issue by moving WAITING<->coro adapter further up the stack

…actor-resthandler-state-machine-into-coro

…e+waitForFuture

The following handlers are changed:

- RestAgencyHandler
- RestAdminLogHandler
- RestDocumentHandler
- RestGraphHandler
- RestImportHandler
- RestLogHandler
- RestLogInternalHandler
- RestMetricsHandler
- RestReplicationHandler
- RestTransactionHandler
- RestUsageMetricsHandler

…cute+waitForFuture

…actor-rest-handlers-into-coroutines

…actor-resthandler-state-machine-into-coro

…ub.com:arangodb/arangodb into feature/refactor-resthandler-state-machine-into-coro

…actor-resthandler-state-machine-into-coro

… of ::execute()

…rangodb_devel2 into feature/refactor-resthandler-state-machine-into-coro

…actor-resthandler-state-machine-into-coro

…actor-resthandler-state-machine-into-coro

…tely, not lazily, to prevent data races

This reverts commit 976cc74.