[stable/concourse] Upgrade to 3.8.0

[nexeck]

This PR will upgrade concourse to version 3.8.0

[k8s-ci-robot]

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[nexeck]

/assign @viglesiasce

[viglesiasce]

cc @william-tran for additional review

/ok-to-test

[mattfarina]

Should the image tag in the readme be updated as well?

[william-tran]

I was working through stability issues with our upgrade to 3.8 but I think we're looking good now. The issue is caused by the reduction of available DB connections for worker scheduling requests, from a shared pool of 64 with API requests, to each having their own pool of 32 DB connections. This forced us to increase the concourse-web replicas from 1 to 3, which resulted in lots of 'unknown handle' errors being logged by workers from multiple concourse-webs doing garbage collection on the same volumes. This would cause the workers to restart unnecessarily. I'd like to lump in the chart changes that improve stability along with a 3.8.0 upgrade.

[nexeck]

@mattfarina i have updated the README.

[mattfarina]

@nexeck I'd like to wait for @william-tran and @viglesiasce on this one as they are the maintainers of the chart itself. If they don't get to it I (or one of the other chart repo maintainers of which @viglesiasce is one) will come back around to it.

[william-tran]

I've made another PR #3203 that supersedes this one, as going to 3.8 requires changes to how we manage worker lifecycle.

[nexeck]

Closed, see #3203