Adding `partOf` linking to Manifests and Collections

[markpbaggett]

While looking for relevant works to test the content search service with, I noticed that we do not currently add partOf links from manifests to the Internet Archive collections they belong to even though that data seems to be available in the metadata service. For instance, cc4ia-Polar_Plunge_Promo_-_2018 includes the 3 collections it belongs to in metadata.collections:

"collection": [
      "cc4ia",
      "community_media",
      "newsandpublicaffairs"
    ]

Why not add links to each like so in partOf:

• cc4ia
• community_media
• newsandpublicaffairs

Similarly, each Collection also links to its collection via metadata.collection like with cc4ia:

"collection": [
      "community_media",
      "newsandpublicaffairs",
      "movies"
    ]

Why not link here too?