Document `SHOW BACKUP CONNECTION <location>`

[benbardin]

Benjamin Bardin (benbardin) commented:

Included in 23.1+

Tests bandwidth from each node in a cluster to the specified cloud storage location, of the form "s3://..." (also works for GCP and Azure)

SHOW BACKUP CONNECTION <location> will return a table like

node |                     locality                     | read_speed  | write_speed
-------+--------------------------------------------------+-------------+--------------

Jira Issue: DOC-10392