MODIFY Exchange article to document the config editor pref for Graph API

[rtanglao]

• We may not need an article edit, possibly link to a wiki page (like we did in the early days of EWS support ) since it is still early days for Graph API in Thunderbird
• this will be ON by default in TB 154 as of the writing of this github issue :-) Could of course move this to 155 or later.
• Not sure when it will be have a UX for this instead of the config editor
• SUMO KB article to edit: Thunderbird and Exchange

[eleanxr]

* Not sure when it will be have a UX for this instead of the config editor

Just to be clear, I don't think any additional UX is needed for this. Enablement/disablement of Graph is currently an about:config pref that is enabled only in daily, but once we turn it on in monthly 154, we already have the UX for autodiscovery/manual config of Graph accounts, so in the chat, the only pref I was referring to was the global enablement pref.