streamline and simplify SVM and MVM custom parameter file UX

[stscijgbot-hstdp]

Issue HLA-795 was created on JIRA by Michael Dulude:

AS it stands, using custom parameter files with the SVM and MVM pipelines is a conusing experience at best. This ticket aims to update code to make the process less confusing and easier to use.

[stscijgbot-hstdp]

Comment by Michele De La Pena on JIRA:

There is no demand for this.  If it is desired to change configuration value settings, users typically just use the default files.