automate metadata updates

[schifferl]

Automate metadata updates with a GitHub action that is run weekly by cron on Wednesday at 12:00 EST in both the latest release (e.g. RELEASE_3_15) and devel (i.e. master) branches of the GitHub repository. It should run inside the appropriate Bioconductor Docker container and open a pull request against the appropriate branch. From the package repository, the necessary steps in R are as follows.

base::source("data-raw/sampleMetadata.R")
roxygen2::roxygenize()

The pull request should be titled "update metadata files", be assigned to me (@schifferl), designate me (@schifferl) as the reviewer, have a commit message of "update metadata files", and have the label "Pull Request". Finally, the action itself should be named "update-metadata", as this is a replacement of an earlier action that did not accomplish the intentions stated herein.