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/config/crawler/cronjob/cronjob.yaml

@@ -12,6 +12,7 @@ spec:
           containers:
           - name: crawler
             image: gcr.io/kustomize-search/crawler:latest
+            imagePullPolicy: Always
             env:
             - name: GITHUB_ACCESS_TOKEN
               valueFrom:

api/internal/crawl/config/crawler/job/job.yaml

@@ -9,6 +9,7 @@ spec:
       containers:
       - name: crawler
         image: gcr.io/kustomize-search/crawler:latest
+        imagePullPolicy: Always
         env:
         - name: GITHUB_ACCESS_TOKEN
           valueFrom: