Support a way to skip implied get after put.

[evanchaoli]

Changes proposed by this PR

closes #3299

• done

Notes to reviewer

There have been much such requests, and I fully understood why implied get is needed in order to keep a resource fresh.

But we may also honor reality. There are a lot of put only resources running in pipelines, mostly about notifications, like put: email, put: slack, etc. Implied get just run an empty container, and plug nested image-check + image-get. We have noticed that Intermittently implied get happened to be placed on a busy worker thus stuck for some time, but they didn't do anything, which hurts stability of build execution.

Adding such an option to opt-out implied get will

• eliminate unnecessary failure points, thus improve build stability
• reduce build execute time
• save worker resources

The other reason I reopen the issue is that, Concourse proposed other approaches to solve the problem, but now those approaches seem to be no ETA anymore.

If you agree to merge this PR, I can update docs as well.

Release Note

• Added no_get option to put step to skip implied get. For example:

  - put: email
    no_get: true
    params:
      ...

[simonjohansson]

This is such a simple fix to an annoying thing when you don't need a get for put only resources... :)

Please merge!

[simonjohansson]

Thx @xtremerui :)

[evanchaoli]

@xtremerui I just rebased the code, hopefully tests would pass.

[xtremerui]

LGTM!

[evanchaoli]

@xtremerui As you have approved this PR, please go ahead merge it. I am not going to apply a patch of this PR to our prod.

[xtremerui]

@evanchaoli please create a PR to update the doc