[tsp-client] Add alternate emitter path information in tsp-client metadata file

Host the list of emitters and their corresponding paths in the metadata file. Then tsp-client will read this config file first and know which emitters are supported by this repo, then the tool will do the look up in tspconfig.yaml for the first entry that matches an emitter in that list. Giving preference to the list order. So the default emitter would be the first in the list and so on until a match is found in tspconfig.yaml. Per our offline teams chat having 2 emitters for the same language in tspconfig.yaml is wrong and we should be validating against this in the specs repo. We also agreed grabbing the first entry that matches in the tspconfig.yaml file.

> NOTE: The teams chat also noted that at some point in the future we may choose to allow multiple entries for a single language, but we will not track that until it becomes an issue we need to support. Wes' comment related to this: "If we do need to support multiple ones in the future we can have tsp-client iterate and run each matching one found in the tspconfig".

cc @JoshLove-msft @weshaggard