Allow setting the download mode file from the helm chart

[arschles]

Is your feature request related to a problem? Please describe.

The only way to set the download mode file from the helm chart currently is to set it with configEnvVars.ATHENS_DOWNLOAD_MODE="base64:<base64 encoded file>". This obviously requires you to base64 encode the download file before putting it into the helm chart.

You can also point Athens to an existing download mode file on disk, but configEnvVars doesn't give you a way to mount a download mode file (i.e. from a config map)

Describe the solution you'd like

I'd like to allow for two things in the helm chart

• Be able to write the download mode file in clear TOML, without base64 encoding it. When you do this, the chart takes care of creating all necessary config maps and mounting, etc...
• Be able to just point the chart at an already existing config map and have the chart take care of all the necessary mounting, etc...

Describe alternatives you've considered

Not doing this and just sticking with the base64: strategy

Additional context

cc/ @dsexton @dylan-bourque @twexler since we talked about this on slack

[arschles]

I will work on this next week, unless someone would like to work on it in that time frame

[wenerme]

Current syntax is configEnvVars.ATHENS_DOWNLOAD_MODE="custom:<base64 encoded file>", should add a note to values.yaml

[wenerme]

@arschles How about treat ATHENS_DOWNLOAD_MODE without prefix as the content of download mode file, this will be way easier

configEnvVars can already ref from secret or configMap, allowed plain hcl in env is ok.

[dylan-bourque]

I very vaguely remember this conversation, but 👍 from me. Seems like a reasonable change.

[DrPsychick]

related to #8