translate env vars if found within file string

[jmclean-starburst]

What this PR does / why we need it:
ArgoCD will pass in a values file that is escaped; this means that any env variables that may exist within the argocd-repo-server cannot be used. In our case, rather than adding the token in clear text to the values.yaml file (remote fetch), we can leverage an environment variable (such as $GITHUB_TOKEN) if it is already existing within that env

Example:
if you supply the string secrets://https://$GITHUB_TOKEN@raw.githubusercontent.com/org/repo/ref/pathtofile.yml to the Argo values files array and the secret GITHUB_TOKEN exists within the argocd-repo-server, it will be injected into the URL.

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #

Special notes for your reviewer:

PR Readiness Checklist:

Complete these before marking the PR as ready to review:

• the CHANGELOG.md release notes have been updated to reflect any significant (and particularly user-facing) changes introduced by this PR

[jmclean-starburst]

Not sure why linting is erroring, would love some feedback

[jkroepke]

Not sure why linting is erroring

The diff explains me that shfmt expects just one space between code and comment.

In general, I don't know if I like to use eval there. Something like https://$(command)/ would also evaluate and executed. This may lead to unwanted code executions. -> https://mywiki.wooledge.org/BashFAQ/048

Normally, I would prefer to use envsubst here. It just substitute the variables and ignore sub shell syntax like $().

On top, it looks like, eval is not compatible with windows paths and other wired path names.

[jmclean-starburst]

one "gotcha" here that may break folks, is I had to add gettext-base to the installer for the ArgoCD custom image. updated with your recommendation to use envsubst

[jkroepke]

I agree. This is breaky.

I looked for alternatives and found this one: https://stackoverflow.com/a/40167919 It still based on shell builtin eval, but it does some sanity checks.

It still feels a little bit risky for me. I'll add this behind a toggle flag. User that want this feature can enable this. Checkout #169 for the code. It's not done yet and tests are missing for that case.

[jkroepke]

Closer in favor of #169