Use alpine docker image for base

[glensc]

Image size reduction:

• 119MB -> 35.4MB
• 123MB -> 63.6MB
• 123MB -> 26.7MB

tasks

• [x] solve ext-mongodb
• [x] needs PHP < 7.4

[glensc]

Back to Draft.

Using alpine:edge to get ext-mongodb, but alpine:edge pulls php 7.4, and PHP 7.4 errors out with accessing null as an array.