ENH Require sudo mode to edit the site config form

[emteknetnz]

Issue silverstripe/silverstripe-admin#1898

[GuySartorelli]

When we talked about this, we agreed that this would only be for the "access" tab, or for the access controls in that tab. There's already permissions controlling access to this model as a whole.

[emteknetnz]

My memory of this was "try and get it to work for just a single tab, and if that proves to be too difficult just put it on everything", and it quickly proved to be too difficult. I'm assuming that editing siteconfig is very infrequent operation so the UX downside here should be very low

The permissions controlling access to the model is irrelevant, the whole point of this is to prevent XSS style attacks on users who do have access

[GuySartorelli]

Putting the discussion about tab vs model aside for now, if we're not protecting the access controls in SiteTree and File, we shouldn't protect them here (continuing the discussion from silverstripe/silverstripe-admin#1898 (comment))

It's sending mixed messages - "we think access controls are privilege escalation" in siteconfig but "we think access controls are not privilege escalation" in the individual records, when they control the same thing.

An XSS attack could give basically the same level of access to pages and files by targetting the records directly as it can via siteconfig.

[emteknetnz]

Fair enough. Will close PR.