Ensure parity between code and docker images.

[mbtamuli]

Currently there is no parity between the code and the Docker images. We can do the following changes

Branching for EasyEngine v4.

Release tags - public usage. easyengine.phar
Master branch - stable at all times. easyengine-nightly.phar
Develop branch - may have code that breaks things. easyengine-edge.phar

Docker image tags.
( Will be built from EasyEngine/dockerfiles repo )

easyengine/php:<semver> - Tagged separately from EasyEngine. Used by easyengine.phar.
easyengine/php:nightly - Built from master branch. Used by easyengine-nightly.phar. Works consistently with easyengine-nightly.phar.
easyengine/php:edge - Built from develop branch. Used by easyengine-edge.phar. The Docker image may have inconsistency with the phar.

For release tag(default): ee cli update [--stable]
For master code: ee cli update --nightly
For develop code: ee cli update --edge

We'll also pin the docker image with the image digest.
We can put this in the CI,

docker pull easyengine/php:v4.0.0-beta.6
docker inspect --format='{{index .RepoDigests 0}}' easyengine/php:v4.0.0-beta.6

The output will be a hash like
easyengine/php@sha256:29934af957c53004d7fb6340139880d23fb1952505a15d69a03af0d1418878cb

[mrrobot47]

Need to remove -nightly tagged images from EasyEngine nightly builds completely. Docker images will have their own versioning independent of EasyEngine versioning. This will solve the parity issue.