feat: support official docker images

[varl]

Started with the makeDockerImage resolutions for supporting channels and versions from https://hub.docker.com/u/dhis2.

• Adds support for official dhis2 docker images in different channels (core, core-dev, core-canary)
• Adds --db-version <string>
• Adds --variant <array>
• Adds --channel <string>
• Adds tests for configuration merging and generating docker image names

Combos

# 2.32 works for both dhis2 and db version
d2 cluster up 2.32 \
  --channel canary

# custom images require explicit context
d2 cluster up custom \
  --image amcgee/dhis2-core:dev-alpine \
  --db-version 2.32 \ 
  --seed

# sometimes the dhis2 and db versions do not match
d2 cluster up stable \
  --dhis2-version 2.31.4 \
  --db-version 2.30 \
  --seed

# dhis2 version can be used for db version if it matches
d2 cluster up 232-dev \
  --channel dev \
  --dhis2-version 2.32 \
  --seed

Save per cluster configuration

To allow for subsequent startups without all the switches we need a mechanism (e.g. #53) to save the configuration first passed to the up command.

So first time the cluster is created it stores the config in e.g. ~/.cache/d2/d2-cluster/dev/configCache.json

This enables:

d2 cluster up dev \
  --custom-context \
  --channel dev \
  --dhis2-version master \
  --db-version dev \
  --seed

d2 cluster down dev

d2 cluster up dev
# will use the `configCache`

Mentioning it here to note that implementing that is out of scope for this PR, but there are plans to do it.

[varl]

The second empty object is going to be replaced with the per-cluster cached configuration. The cluster object is the default configuration from ~/.config/d2/config.js.

[amcgee]

This looks really great!! I made a couple minor comments, but happy with it as is as well. Also yay tests!!

[varl]

@amcgee did three changes:

1. split the makeEnvironment in twain; resolveConfiguration and makeEnvironment.
2. added default where important (channel and port) to the description.
3. changed the --variant switch to accept a string, so users would have to say --variant tomcat-alpine, this works around the ordering problem with an array switch.

[amcgee]

Should this use the same defaults logic as the other properties? So basically that would mean removing the if !substitutes.channel check from makeDockerImage and adding channel: 'stable' to defaults ...?

[varl]

Sure, I can change the defaults.channel to stable and use the same logic. 👍

I cannot remove the !substitutes.channel check though since the makeDockerImage function doesn't do the configuration resolution itself, and if the function is used with a substitution object which doesn't pass in the channel, it won't get replaced with an empty string. The tests catch this situation and started to error out.

It would have been a bit simpler if the stable repo was called core-stable and not just core, but I'd rather have a little bit of extra complexity here and a nicer repo name than the other way around.

[varl]

0929a64

[amcgee]

This is great! Tested locally, working like a charm. And now that @vilkg has pushed stable releases to dhis2/core the world is starting to make sense :-D

[dhis2-bot]

🎉 This PR is included in version 1.2.0 🎉

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