Mulitple improvements of the crawler

1) Set document IDs to avoid duplicating documents;
2) Set the `creationTime` field of each document in the index;
3) set the `values`, `kinds` and `identifiers` fields for all documents;
4) Add a `Copy` method into the `Document` struct: this fixes the issue
where all the documents existing in the index point to the same Document
object;
5) Avoid using keystore redis;
6) Set imagePullPolicy to `Always` for crawler jobs.

api/internal/crawl/crawler/github/queries.go

@@ -7,7 +7,7 @@ import (
 )
 
 const (
-	perPageArg     = "per_page"
+	perPageArg = "per_page"
 )
 
 const githubMaxPageSize = 100