Update UI screenshots in Pipeline documentation

[kmartens27]

Describe your use-case which is not covered by existing documentation.

There are pages in the Pipeline section of documentation that have older screenshots of Jenkins' UI. The current screenshots may show either older terminology "manage credentials" vs the current "credentials" or older versions of the UI where icons are full color as opposed to the modernized versions of what now appear. The screenshots may also contain outdated terminology such as "master" or "slave" where the replacements of "controller" and "agent" should be present. Refer to the Inclusive Naming information for additional details on this.

The screenshots would need to follow the guidelines outlined in the Jenkins contributing guide, along with any necessary highlighting/call outs that might be relevant to the screenshot.

If you are interested in working on this, the quickstart tutorials can help get you up to speed and running Jenkins in no time.

Reference any relevant documentation, other materials or issues/pull requests that can be used for inspiration.

Pages that need screenshot updates:

Getting started with Pipeline
Running Pipelines
Branches and Pull Requests
Using Docker with Pipeline
Extending with Shared Libraries
Pipeline Development Tools
Pipeline as Code