`iox-debug` header

[jstirnaman]

Document the new iox-debug optional header that "reveals" system.queries and other system tables:

https://github.com/influxdata/influxdb_iox/commit/31b881376057bf7e50381519c4f5c9e15c1aee33

Relevant URLs

• https://github.com/influxdata/influxdb_iox/commit/31b881376057bf7e50381519c4f5c9e15c1aee33
• https://github.com/influxdata/influxdb_iox/blob/43078576b8b2896b3c148b21e6cc5c208a4bf3ea/generated_types/protos/influxdata/iox/querier/v1/flight.proto#L49
• https://docs.influxdata.com/influxdb/cloud-dedicated/reference/internals/system-tables/

[jstirnaman]

Completed for Cloud Dedicated with #5143