Feat: Bolt 5.8 - home db cache & optimistic routing

[robsdedude]

Introducing support for Bolt 5.8, which (among other things) makes the server echo back the resolved home/default db on starting a transaction as well as a connection hint whether server-side routing (SSR) is enabled. If so, the echoed db can be used together with an optimistic home db cache to guess a client-side route (optimistic routing - falling back to SSR on wrong guesses). This feature saves a round-trip under the following conditions (all must be fulfilled):

• Server has SSR enabled
• Sever supports Bolt 5.8
• A fresh (yet unused) session without an explicitly configured target database starts its first transaction (auto-commit or explicit)
• There is a cache entry for the current user.
  How exactly "current user" is defined is left as an implementation detail. Currently, this is in order of descending precedence:
  • the impersonated user if any
  • else the session auth token (for basic auth, only the principal is considered) if any
  • else some fallback key representing the driver-level user.