Currently, tested instances type described in installation doc[1][2][3] are synced up from installer repo master branch. If we add new instance type in installer master branch, it will reflect in all versions of installation doc.

Actually, some instance types are supported and tested starting from specific versions, but not on all versions. For example, azure confidential supported instance types are added on 4.14+ (https://github.com/openshift/installer/pull/7639), and on 4.13 and previous version, installer exit with error that those types are not supported yet.

Installation doc should sync up tested instance type from installer repo on matched branch. For example, 4.15 installation doc gets instance type from installer openshift-4.15 branch.

[1] https://docs.openshift.com/container-platform/4.15/installing/installing_aws/installing-aws-customizations.html#installation-aws-tested-machine-types_installing-aws-customizations
[2]https://docs.openshift.com/container-platform/4.15/installing/installing_azure/installing-azure-customizations.html#installation-azure-tested-machine-types_installing-azure-customizations
[3]https://docs.openshift.com/container-platform/4.15/installing/installing_gcp/installing-gcp-customizations.html#installation-gcp-tested-machine-types_installing-gcp-customizations

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