docs: use capa as capi operator example

[salasberryfin]

Description

The existing example in Turtles' CAPI Operator docs for installing a CAPIProvider refers to upstream's CAPI Operator book and Azure Provider. As CAPZ is not yet an officially supported provider in Turtles, we should use a supported provider in the example instead. This changes it from CAPZ to CAPA.

[furkatgofurov7]

Looks good, it seems there is another mention of azure here https://turtles.docs.rancher.com/contributing/install_capi_operator/?_highlight=azure#install-manually-with-helm-alternative that needs update

[salasberryfin]

Thanks for noticing @furkatgofurov7. I updated those references too.