Jinja templating can be optimised

Creating a new jinja Loader and Environment for each template file is a little waste of resources.

We could create a single Environment for the whole script and generate overlays for extras like addons and admin-tools with specific loader, environments are passed down to genTemplate:

def cli():
    default_loader = FileSystemLoader('templates')
    default_env = Environment(loader=default_loader)
    # […]
    
# gen_socle() use defaults

def gen_addon(ctx, name=None, addon_config=None):
    addon_path = join('addons', name)
    # Addons load templates from its directory first then fallback to top level `templates/`
    addon_loader = FileSystemLoader([
        join(addon_path, 'templates'),
        join(root_dir, 'templates')
    ])
    addon_env = default_env.overlay(loader=addon_loader)
    # […]

def gen_admin_tool(ctx, name=None, admin_tool_config=None):
    admin_tool_path = join('admin-tools', name)
    # Admin_Tools load templates from its directory first then fallback to top level `templates/`
    admin_tool_loader = FileSystemLoader([
        join(admin_tool_path, 'templates'),
        join(root_dir, 'templates')
    ])
    admin_tool_env = default_env.overlay(loader=admin_tool_loader)
    # […]