Support post gen edpm kustomize scripts

This patch introduces a mechanism to run an arbitrary script on the
`edpm_deploy_prep` target after the `kustomization.yaml` file has been
created by the `gen-edpm-kustomize.sh` script.

This provides a flexible mechanism to modify things in the kustomization
that are not currently possible.

An example is to use a different ansible host for deployment than the IP
that will be used as the `ctlplane` network IP.

The variable used to define the location of the script is
`EDPM_POST_GEN_SCRIPT`.

Example of usage:

```
$ make edpm_deploy \
  DATAPLANE_POST_GEN_SCRIPT="$(realpath ./scripts/change-ansible-hosts.sh)"
```

And the contents of `change-ansible-hosts.sh` are:

```
sed -i "s/value: 192.168.122.100/value: 192.168.1.13/" kustomization.yaml
```

Makefile

@@ -832,6 +832,7 @@ edpm_deploy_prep: export BRANCH=${OPENSTACK_BRANCH}
 edpm_deploy_prep: export HASH=${OPENSTACK_COMMIT_HASH}
 edpm_deploy_prep: export EDPM_TLS_ENABLED=${DATAPLANE_TLS_ENABLED}
 edpm_deploy_prep: export EDPM_NOVA_NFS_PATH=${DATAPLANE_NOVA_NFS_PATH}
+edpm_deploy_prep: export EDPM_POST_GEN_SCRIPT=${DATAPLANE_POST_GEN_SCRIPT}
 ifeq ($(NETWORK_BGP), true)
 ifeq ($(BGP_OVN_ROUTING), true)
 edpm_deploy_prep: export BGP=ovn

scripts/gen-edpm-kustomize.sh

@@ -222,4 +222,8 @@ fi
 
 kustomization_add_resources
 
+if [ -n "${EDPM_POST_GEN_SCRIPT}" ]; then
+    . "${EDPM_POST_GEN_SCRIPT}"
+fi
+
 popd