RFC 235: Add code intel postgres container

[efritz]

A step towards RFC 235: Move LSIF data to Postgres.

Add a new copy of the postgres container to be used as a code intel-specific database. Configure the frontend to point to this new database (in addition to the current pgsql container).

Partially implements https://github.com/sourcegraph/sourcegraph/issues/13883 along with sibling PRs https://github.com/sourcegraph/sourcegraph/pull/13904 and sourcegraph/deploy-sourcegraph-docker#153.

[pecigonzalo]

LGTM. Diffs to pgsql:

❯ diff base/pgsql/pgsql.ConfigMap.yaml base/codeintel-db/codeintel-db.ConfigMap.yaml
9c9
<   name: pgsql-conf
---
>   name: codeintel-db-conf

❯ diff base/pgsql/pgsql.Service.yaml base/codeintel-db/codeintel-db.Service.yaml
8c8
<     app: pgsql
---
>     app: codeintel-db
11c11
<   name: pgsql
---
>   name: codeintel-db
18c18
<     app: pgsql
---
>     app: codeintel-db

❯ diff base/pgsql/pgsql.Deployment.yaml base/codeintel-db/codeintel-db.Deployment.yaml
9c9
<   name: pgsql
---
>   name: codeintel-db
16c16
<       app: pgsql
---
>       app: codeintel-db
23c23
<         app: pgsql
---
>         app: codeintel-db
37c37
<         image: index.docker.io/sourcegraph/postgres-11.4:3.16.0@sha256:63090799b34b3115a387d96fe2227a37999d432b774a1d9b7966b8c5d81b56ad
---
>         image: index.docker.io/sourcegraph/codeintel-db@sha256:63090799b34b3115a387d96fe2227a37999d432b774a1d9b7966b8c5d81b56ad
82c82
<           claimName: pgsql
---
>           claimName: codeintel-db
86c86
<           name: pgsql-conf
---
>           name: codeintel-db-conf

❯ diff base/pgsql/pgsql.PersistentVolumeClaim.yaml base/codeintel-db/codeintel-db.PersistentVolumeClaim.yaml
7c7
<   name: pgsql
---
>   name: codeintel-db