request(base-images): provide docker base images for php-alpine

[keithy]

FROM codecasts/alpine-3.9:php-7.3 not present on hub.docker

[othercorey]

I can only find alpine-3.7 and alpine-3.6 listed in the repositories

[glensc]

i reported this as well to @hernandev in the commit:

• 5744597#r33657141

however, you can build the image yourself:

1. modify .env
2. ./build.sh sandbox

[FernandoMiguel]

any update on this ticket

[hernandev]

we are not building base images as of right now, we should be doing that once again, changing this to a request issue