feat: add default security permissions policy

wowchemy/layouts/index.headers

@@ -1,6 +1,7 @@
 {{- $csp_policy := site.Params.security.csp.policy | default "" -}}
 {{- $csp_report_only := site.Params.security.csp.report_only | default false -}}
-{{- $permissions_policy := site.Params.security.permissions.policy | default "" -}}
+{{- $default_perms := "accelerometer=(), camera=(), geolocation=(), gyroscope=(), magnetometer=(), microphone=(), payment=(), usb=()" -}}
+{{- $permissions_policy := site.Params.security.permissions.policy | default $default_perms -}}
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