Get Collection by wildcards

[stuartc]

Re: #2190

Add a function that retrieves a list of items from a collection based on a key with wildcards.

Given this rough example:

{op: "get", collection: "collection-name", key: "foo:*:bar*"}

The resulting query might look something like this:

SELECT * FROM collection_items 
  -- join collections by name
  WHERE key LIKE "foo:%:bar%"

Note that a simple BTREE index will help up until the first wildcard appears, using a GIN index with the pg_trgm extension will allow for indexing to work with more than one wildcard:

CREATE INDEX idx_my_keys_trgm ON my_keys USING GIN (key_name gin_trgm_ops);

Acceptance criteria

• A new function in the Collections context that returns a stream of items with keys matching the query.
• Must be injection proof, i.e. use the like macros from Ecto.