Add documentation for kong_consumer_key_auth

Author: andrew-bulford-form3

docs/resources/consumer_key_auth.md

@@ -0,0 +1,28 @@
+# kong_consumer_key_auth
+
+Resource that allows you to configure the [Key Authentication](https://docs.konghq.com/hub/kong-inc/key-auth/) plugin for a consumer.
+
+## Example Usage
+
+```hcl
+resource "kong_consumer" "my_consumer" {
+  username  = "User1"
+  custom_id = "123"
+}
+
+resource "kong_plugin" "key_auth_plugin" {
+  name = "key-auth"
+}
+
+resource "kong_consumer_key_auth" "consumer_key_auth" {
+  consumer_id = kong_consumer.my_consumer.id
+  key         = "secret"
+  tags        = ["myTag", "anotherTag"]
+}
+```
+
+## Argument Reference
+
+* `consumer_id` - (Required) the id of the consumer to associate the credentials to
+* `key` - (Optional) Unique key to authenticate the client; if omitted the plugin will generate one
+* `tags` - (Optional) A list of strings associated with the consumer key auth for grouping and filtering