default `CONCOURSE_VAULT_AUTH_PARAM` to set if the corresponding secret is set

[aoldershaw]

Why do we need this PR?

223 introduced a breaking change - before, when the vault backend was set to approle, we'd set CONCOURSE_VAULT_AUTH_PARAM. now, it's only set if useAuthParam is explicitly set to true, since it defaults to false. this means that upgrading from 15.0.x -> 15.1.x unset that param, unless you knew to enable useAuthParam (which wasn't documented in the release notes).

it seems more sane to set the auth param if either you explicitly opt-in (by enabling useAuthParam) OR if you set the vault auth param in the secret, and didn't explicitly opt-out by setting useAuthParam to false

Changes proposed in this pull request

• No default for .Values.concourse.web.vault.useAuthParam - distinguish between unset and false
• Set CONCOURSE_VAULT_AUTH_PARAM from secret if Values.concourse.web.vault.useAuthParam is set to true or if .Values.secrets.vaultAuthParam is set
  • Note: we still want useAuthParam, since the secret may be created external to helm, and we still need some way of indicating we want that secret

Contributor Checklist

• [ ] Variables are documented in the README.md
• [ ] Which branch are you merging into?
  • master is for changes related to the current release of the concourse/concourse:latest image and should be good to publish immediately
  • dev is for changes related to the next release of Concourse (aka unpublished code on master in concourse/concourse)

Reviewer Checklist

This section is intended for the core maintainers only, to track review progress. Please do not fill out this section.

• [ ] Code reviewed
• [ ] Topgun tests run
• [ ] Back-port if needed
• [ ] Is the correct branch targeted? (master or dev)