Why was categories removed from BPP level and added to provider?

[joffinjoy]

In earlier versions of the schema, categories was an array of object at BPP level as shown below:

{
	"catalog": {
		"descriptor": {},
		"categories": [],
		"providers": [],
		"fulfillments": []
	}
}

But in the current 1.x core-spec schema, this categories has been moved from root (BPP) level to provider level like this:

{
	"catalog": {
		"descriptor": {},
		"providers": [{
			"categories": [{}],
			"items": []
		}],
		"fulfillments": []
	}
}

1. What was/were the reason(s) for this change? We are trying to understand the implication this has on filtering based on categories and any change in the meaning/definition of categories across multiple providers.

2. Are categories supposed to be a globally accepted enum across the entire DSEP network (Standard set of categories like languages)?

Probably related: #336

cc: @ravi-prakash-v, @aks30, @vijiurs, @kiranharidas187