Link discrepancy possible between /collections and /collection/{id}

[moradology]

It looks like the pgstac implementations of all_collections and get_collection don't always agree in the link field that each produces for a given collection.

It is possible that extra_links should be used here although that argument is not provided in the details case here and is thus not likely to be the culprit.

Example from list endpoint (for a given collection):

"links": [
  {
    "rel": "license",
    "href": "https://www.fsa.usda.gov/help/policies-and-links/"
  }
]

Example from detail (the above mentioned collection) endpoint:

"links": [
  {
    "rel": "items",
    "type": "application/geo+json",
    "href": "http://localhost:8080/stac/collections/usda-naip/items"
  },
  {
    "rel": "parent",
    "type": "application/json",
    "href": "http://localhost:8080/stac/"
  },
  {
    "rel": "root",
    "type": "application/json",
    "href": "http://localhost:8080/stac/"
  },
  {
    "rel": "self",
    "type": "application/json",
    "href": "http://localhost:8080/stac/collections/usda-naip"
  }
],

[moradology]

Closed in #269