Set Ghost user-agent header for got requests (#10424)
Set Ghost user-agent header for got requests (#10424)

no-issue

Currently the `user-agent` header is the for outgoing webhook calls is the `got` default: `User-Agent: got/8.3.2 (https://github.com/sindresorhus/got)`.

This is pretty unfriendly to the receiver of the webhook who may wish to perform analytics on calling systems, implement security features based on calling system or take action based on different versions of a client.

This PR sets the header to: `User-Agent: Ghost/2.12.0 (https://github.com/TryGhost/Ghost)` which is much more descriptive. 
kevinansfield/Ghost,bitjson/Ghost,ErisDS/Ghost,kevinansfield/Ghost,bitjson/Ghost,JohnONolan/Ghost,Kikobeats/Ghost,ErisDS/Ghost,TryGhost/Ghost,e10/Ghost,janvt/Ghost,janvt/Ghost,JohnONolan/Ghost,Kikobeats/Ghost,Gargol/Ghost,e10/Ghost,ErisDS/Ghost,JohnONolan/Ghost,TryGhost/Ghost,Gargol/Ghost,TryGhost/Ghost,Kikobeats/Ghost,kevinansfield/Ghost