Add ESG external subnet selectors support

[camrossi]

• Add external_subnet_selectors to endpoint security groups
• Support for external subnet selection in ESG configuration
• Update documentation and examples for external subnet selectors
• Include validation and proper variable definitions

[robvand]

Few remarks:

The shared bool is not idempotent:

  # module.aci.module.aci_endpoint_security_group["ts-ocp-1/openshift/egress"].aci_rest_managed.fvExternalSubnetSelector["10.61.6.80/28"] will be updated in-place
  ~ resource "aci_rest_managed" "fvExternalSubnetSelector" {
      ~ content     = {
          ~ "shared" = "yes" -> "true"
            # (1 unchanged element hidden)
        }
        id          = "uni/tn-ts-ocp-1/ap-openshift/esg-egress/extsubselector-[10.61.6.80/28]"
        # (4 unchanged attributes hidden)

Value key should probably be ip: for consistency.

[camrossi]

@robvand fixed it
However I only changed from value to ip in the ip_external_subnet_selectors. value was already used in all the other instances so I do not wanna introduce any breaking change. Perhaps a different PR should address this for ip_subnet_selectors

[robvand]

Thanks for the fixes. Seems your PR includes some changes to the set-rule module which should be omitted.

[jmmarquezg]

The internal repo is using "value" instead of "ip" for that attribute. I made some changes and pushed them to this very same PR.
Nothing wrong with the code logic, just to keep consistency across all repos.
I might need you to allow me to send changes to your fork so this changes can be made in this same fork.

[camrossi]

@jmmarquezg I used ip because @robvand pointed out that value is not a very good name for this.
I agreed with Rob and was thinking for values that are ips we should indeed use ip or at least add it as an alias so we can keep backward compatibility perhaps?

[juchowan]

Let's keep it as ip. @jmmarquezg please update the internal repo

[jmmarquezg]

Internal repo now is matching "ip" parameter name

[juchowan]

@jmmarquezg still pending updates in this PR