Create an action to post builds and updates of the website into the Matrix channel

[tommerty]

Going to be fucking about with it from this: https://github.com/marketplace/actions/matrix-channel-message

[tommerty]

Need to set the following:

${{ secrets.MATRIX_SERVER }}
${{ secrets.MATRIX_ROOM_ID }}
${{ secrets.MATRIX_USER }}
${{ secrets.MATRIX_PASSWORD }}