feat(httpsettings): add tls auth option

- Three text areas where the user can paste
in the CA Cert (optional), Client Cert
and Client Key.

- Tooltips for Auth checkboxes with brief
descriptions of what With Credentials and
With CA Cert are.

- Adds popover for TLS Auth header too.

- Aligns gf-form elements as labels and
checkboxes were not aligned before.

- Makes CA Cert optional as it is only
needed for self-signed certs.

public/sass/components/_gf-form.scss

@@ -79,6 +79,10 @@ $gf-form-margin: 0.25rem;
   }
 }
 
+.gf-form-textarea {
+  max-width: 650px;
+}
+
 .gf-form-input {
   display: block;
   width: 100%;
@@ -249,6 +253,10 @@ $gf-form-margin: 0.25rem;
   &--right-normal {
     float: right;
   }
+
+  &--header {
+    margin-bottom: $gf-form-margin
+  }
 }
 
 select.gf-form-input ~ .gf-form-help-icon {