Description of problem

compute.replicas docs replicas: 0 for three-node clusters, but install-config docs have A positive integer greater than or equal to 2. The default value is 3. for compute.replicas.  I dunno if we support 1 there, but seems like either we should drop our nominal requirements and allow any >=0 value, or we should enforce our policy somewhere under validateCompute.

Definition of done:

• Figure out what compute.replicas values are supported.
• Add install-config verification to the installer to require those values, if its different from the currently-implemented >= 0.
• Update docs references to consistently document the actual supported values.

How reproducible

Unclear, because the supported values are unclear.

Steps to Reproduce

Unclear, because the supported values are unclear.

Actual results

Unclear, because the supported values are unclear.

Expected results

Docs describe internally-consistent supported values, and the installer's install-config validation enforces that range.