RFC - Consolidate use of insecure endpoints across controllers

[pjbgf]

Across Flux controllers the use of non-TLS based connections is not consistent.

Controllers that deals only with http and https schemes have no way to block use of the http scheme at controller-level.
Some Flux objects provide an .Spec.Insecure field to enable the use of non-TLS based endpoints, but they don't clearly notify users when the option is not supported (e.g. Azure/GCP Buckets).

A new RFC should be created to establish:

• Controller-level ways to block the use of HTTP endpoints. When enabled, the flag would not allow the use of the non-TLS based connections across all controller-level objects.
• Consistent way to support insecure endpoints and to notify when they are not supported (or it has been blocked at controller level).
• Naming conventions covering flags and object fields.

Related Implementations:

• support plain HTTP OCI registries in HelmRepositories source-controller#828
• [RFC-0004] Allow disabling of insecure HTTP connections for alert providers notification-controller#404