Update pcf-scripts to allow for .js index files

[MathewBur]

Currently pcf-scripts requires the index file of a PCF to be a .ts filetype.

This is due to the node_modules\pcf-scripts\ManifestSchema.json Line 518

"path": { "type": "string", "pattern": "^.+\.ts$", "minLength": 1 },

Could this be changed either by editing the validation condition to allow for .js index files

"path": { "type": "string", "pattern": "^.+\.(ts|js)$", "minLength": 1 },

or adding another option in the node_modules\pcf-scripts\featureflags.json which can be set with the featureconfig.json file.

{
"pcfAllowCustomWebpack": "on",
"pcfAllowJSIndex": "on"
}