Fix worker custom certificats support

[o-orand]

Why do we need this PR?

This PR provided some bug fixes related to #211.

Changes proposed in this pull request

• use consistent mechanism to retrieve certificates in worker-secret.yml removal of worker.additionalCertificates should have been done with 43483576525c8fab2e5af1f3ff41a039b122d433 (included in #244). But it still present in worker-secret.yml.
• use worker.certsPath defined in values.yml instead worker.workerCertsPath (undocumented and not use anywhere else). https://github.com/concourse/concourse-chart/blob/6b13c2077bcdede6ef1615d22eef9d36307e70e7/values.yaml#L2304-L2307

Contributor Checklist

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

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)