Support for Ambassador OSS as an Ingress (#6135)

Support for Ambassador OSS as an Ingress Controller when
settings `ingress_ambassador_enabled: true`.

Signed-off-by: Alvaro Saurin <alvaro.saurin@gmail.com>

roles/kubernetes-apps/ingress_controller/ambassador/README.md

@@ -0,0 +1,37 @@
+# Installation Guide
+
+- [Installation Guide](#installation-guide)
+  - [Ambassador](#ambassador)
+  - [Ambassador Operator](#ambassador-operator)
+  - [Configuration](#configuration)
+  - [Ingress annotations](#ingress-annotations)
+
+## Ambassador
+
+The Ambassador API Gateway provides all the functionality of a traditional ingress controller
+(e.g., path-based routing) while exposing many additional capabilities such as authentication,
+URL rewriting, CORS, rate limiting, and automatic metrics collection.
+
+## Ambassador Operator
+
+This addon deploys the Ambassador Operator, which in turn will install Ambassador in
+a kubespray cluster.
+
+The Ambassador Operator is a Kubernetes Operator that controls Ambassador's complete lifecycle
+in your cluster, automating many of the repeatable tasks you would otherwise have to perform
+yourself.  Once installed, the Operator will complete installations and seamlessly upgrade to new
+versions of Ambassador as they become available.
+
+## Configuration
+
+* `ingress_ambassador_namespace` (default `ambassador`): namespace for installing Ambassador.
+* `ingress_ambassador_update_window` (default `0 0 * * SUN`): _crontab_-like expression
+  for specifying when the Operator should try to update the Ambassador API Gateway.
+* `ingress_ambassador_version` (defaulkt: `*`): SemVer rule for versions allowed for
+  installation/updates.
+
+## Ingress annotations
+
+The Ambassador API Gateway will automatically load balance `Ingress` resources
+that include the annotation `kubernetes.io/ingress.class=ambassador`. All the other
+resources will be just ignored.