Evaluate and implement yamllint for yaml-related, content-based changes

The current release post process requires that several steps be manually done (including removing spaces at the ends of lines, and proper syntax usage). To better ensure that issues aren't missed, and to reduce the amount of manual steps in processes that involve updates to yaml files, we should evaluate the use of yamllint (https://yamllint.readthedocs.io/en/stable/rules.html) as a checker for YAML files.