[DOCS] Docs need updated for HA masters and key signing

Description
This docs request is in relation to issue [62318]. See the comment linked below.

https://github.com/saltstack/salt/issues/62318#issuecomment-1273311794

Currently, the documentation for running masters in HA modes (Failover and Active/Active) provide potentially conflicting, or at least unclear, information about how the keys on the masters should be configured for authentication.

https://docs.saltproject.io/en/latest/topics/tutorials/multimaster_pki.html
https://docs.saltproject.io/en/latest/topics/highavailability/index.html

Suggested Fix
Update the documentation to clarify when key signing is expected to work and the necessary configuration for the master key pair

Type of documentation
This is for Salt documentation.

Location or format of documentation
https://docs.saltproject.io/en/latest/topics/tutorials/multimaster_pki.html
https://docs.saltproject.io/en/latest/topics/highavailability/index.html

Additional context
This docs request is in relation to issue [62318].

Start by reading the linked comment on issue 62318, then compare topics/tutorials/multimaster_pki.html with topics/highavailability/index.html. Clarify when key signing works and document the required master key-pair configuration consistently in both pages.