add mambaforge installer

[jameslamb]

Contributes to microsoft/LightGBM#4948.

This PR proposes adding support for using mamba instead of conda to install conda packages.

How I tested this

cd dockers/ubuntu-14.04
docker build \
    -t lightgbm/vsts-agent:local \
    -f ./Dockerfile \
    .

Notes for Reviewers

I'd like to push these changes to the dev branch, and test pulling in the new image lightgbm/vsts-agent:ubuntu-14.04-dev pushed to Docker Hub on microsoft/LightGBM#4953.

Per microsoft/LightGBM#4948 (comment), I don't have permissions to create branches here.

@StrikerRUS could you create a dev branch in this repo so I can target this PR at it?

@guolinke if you see this, could you please give me "write" permissions on this repo so I can add branches myself in the future?

[jameslamb]

adding a .dockerignore isn't strictly necessary to add support for mamba, but I think it's generally a good idea and thought now was a good time, given that we're about to test this new image anyway.

For details on this file, you can see https://codefresh.io/docker-tutorial/not-ignore-dockerignore-2/.

Benefits:

• smaller build context = faster builds
• reduced risk of accidentally including unnecessary files
  • smaller images
  • less risk of including secret / sensitive information

[StrikerRUS]

could you create a dev branch in this repo so I can target this PR at it?

Done!

[jameslamb]

Thank you very much! I just updated this to dev, so I think it's ready for review. My proposal is the following:

1. merge this change to dev, so that a new image lightgbm/vsts-agent:ubuntu-14.04-dev will be pushed to Docker Hub
2. in [ci] use conda-forge in Linux and macOS CI jobs microsoft/LightGBM#4953, change .vsts-ci.yml to reference that dev image
3. once it's approved, merge [ci] use conda-forge in Linux and macOS CI jobs microsoft/LightGBM#4953
4. come back here and merge dev into master
5. follow-up PR in LightGBM to change the image reference in .vsts-ci.yml to the non-dev tag (lightgbm/vsts-agent:ubuntu-14.04)

[StrikerRUS]

Thank you! Agree with your plan. Please consider checking my suggestion about paths and filenames renaming below.

[StrikerRUS]

I can't make a suggestion for all these lines, so describing my suggestion just in words.

Let's be explicit here and don't call Mambaforge installation as "Miniconda"/"conda".
Please update lines 86-95 making it clear we are working with mamba[forge]. The only public entrypoint here is CONDA env variable, so don't change its name.

[jameslamb]

sure, works for me!

updated in f75b7a4 and tested that building the image still works

[StrikerRUS]

LGTM!

[StrikerRUS]

dev has been published:

[guolinke]

Thank you @jameslamb , I will give you the write permission.

[jameslamb]

thanks very much @guolinke !