Don't allow additon of template settings when the template is in Not-Ready state

### problem

Don't allow addition of template settings when the template is in Not-Ready state

### versions

ACS 4.22

### The steps to reproduce the bug

1. Login to cloudstack with a admin role

Navigate Images > Template > Register a template > enable “Read Instance settings from OVA”

2. When the template is getting downloaded , its in Not ready state

3. Navigate to template settings and try to add Template settings

4. The template settings gets added

### What to do about it?

CloudStack should thrown exception saying that its unable to add settings when the template is in not-ready state or Settings are read directly from the template

Reproduce the issue through Images > Template > Register a template with “Read Instance settings from OVA” enabled, then try to add template settings while the template is Not-Ready. Trace the template-settings entry point and its validation, and verify that the operation is rejected with an exception or message instead of adding settings.

Written by the indexing model from the issue text.