add multiple process steps

It would be helpful to have the option to add multiple process steps to a release. I think the [template](https://github.com/USGS-R/meddle/blob/d1a4aa288831707b65856995a2d464a399093ad4/inst/extdata/FGDC_template.mustache#L174) would need to be updated, as well as the pipeline to achieve this.