[kong] simplify license secret kubectl command

Enterprise users frequently run into problems with the current way the
secret is created. The files have extensions which cause problem later
on in the deployment and this has taken up a lot of time in debugging
several support tickets.

The new format makes it clear and avoids problems when the file has an
extension or is present in a different directory.

charts/kong/README.md

@@ -467,11 +467,10 @@ configuration can be placed under the `.env` key.
 
 All Kong Enterprise deployments require a license. If you do not have a copy
 of yours, please contact Kong Support. Once you have it, you will need to
-store it in a Secret. Save your secret in a file named `license` (no extension)
-and then create and inspect your secret:
+store it in a Secret:
 
 ```bash
-$ kubectl create secret generic kong-enterprise-license --from-file=./license
+$ kubectl create secret generic kong-enterprise-license --from-file=license=./license.json
 ```
 
 Set the secret name in `values.yaml`, in the `.enterprise.license_secret` key.