Update pipeline execution policy to not save without a file path

The following discussion from !172643 (merged) should be addressed:

• @mfluharty started a discussion: (+1 comment)

  nitpick (non-blocking): This "The file path can't be empty" form validation message doesn't seem to be true 🤔

  Screen_Recording_2024-11-19_at_12.59.34

• the file property is required in the schema, but the UI adds file: '' when the user adds a string and then removes it

Implemenation

• check if file exists and remove file property if it doesn't