Add support for repo configuration using environment variables

[isc-dchui]

Description

• Closes Add support for repo password/token via environment variable #1178
• Adds -password-env <var> and -token-env <var> flags to read from the var environment variable.
• Throws an error if the specified env var is not set or empty
• Throws an error if more than one password or token flag is used

Testing

• Added a unit test
• Manually tested by setting a env-var and using -password-env

Checklist

• This branch has the latest changes from the main branch rebased or merged.
• Changelog entry added.
• Unit (zpm test -only) and integration tests (zpm verify -only) pass.
• Style matches the style guide in the contributing guide.
• Documentation has been/will be updated
  • Source controlled docs, e.g. README.md, should be included in this PR and Wiki changes should be made after this PR is merged (add an extra issue for this if needed)
• Pull request correctly renders in the "Preview" tab.