License Key - optional heartbeat feedback data

We need to define what data MaxScale's license heartbeat sends back to
mariadb.com, with an emphasis on transparency: the payload must be fully
documented, inspectable by the customer and anonymised.

Ideas:
Environment / deployment:

• MaxScale version
• OS and distro
• Container vs. VM deployment
• CPU count
• RAM

Usage / configuration shape:

• Routers and filters in use (which ones, not their configured values)
• Number of connected backends
• MariaDB Server version(s) in use across connected backends

Explicitly OUT of scope — must never be collected:

• Passwords
• Usernames
• Object names (databases, tables, schemas, etc.)

By default we should include these on for maxscale trial and off for enterprise
[maxscale]
disable_heartbeats=true