Can't set HASURA_GRAPHQL_METADATA_DATABASE_URL to the same URL as HASURA_GRAPHQL_DATABASE_URL when Updating to v2.0.9 from v1.3.2 using Docker

### Version Information

Server Version: updating from v1.3.2 to v.2.0.9
CLI Version (for CLI related issue): Not Related to CLI, i think

### Environment
OS: CentOS 7
running on Docker

### What is the expected behaviour?
updating to v2.0.9 by just changing the image used in docker-compose.yml and the image will take care of everything

### Keywords
Updating
Migrating
v2

### What is the current behaviour?
I am trying to update my development hasura server before trying to do it on my production server. It's running on docker using v1.3.2 image and I want to update it to v2.0.9 image

Here is the docker-compose.yml I'm using

```yaml
version: '3.6'
services:
hasura-engine:
image: hasura-graphql-engine:v2.0.9
container_name: hasura-engine
ports:
- "5001:8080"
expose:
- "8080"
environment:
HASURA_GRAPHQL_DATABASE_URL:
HASURA_GRAPHQL_METADATA_DATABASE_URL:
HASURA_GRAPHQL_ENABLE_CONSOLE: "true"
HASURA_GRAPHQL_ADMIN_SECRET:
HASURA_GRAPHQL_ENABLED_LOG_TYPES: startup, http-log, webhook-log, websocket-log, query-log
HASURA_GRAPHQL_JWT_SECRET:
networks:
default:
ipv4_address:
networks:
default:
external:
name: docker-bridge
```

My understanding from reading the documentation is that i can just change the docker image used in docker-compose.yml and just restart the container and the image will take care of everything.

Previously, I was using a database named postgres as the database connected to the hasura server. The HASURA_GRAPHQL_DATABASE_URL is set to this database URL. After reading [this article](https://hasura.io/docs/latest/graphql/core/deployment/graphql-engine-flags/config-examples.html), I've tried
1. not setting the HASURA_GRAPHQL_METADATA_DATABASE_URL env variable
2. setting the HASURA_GRAPHQL_METADATA_DATABASE_URL to the same URL as HASURA_GRAPHQL_DATABASE_URL
3. setting the HASURA_GRAPHQL_METADATA_DATABASE_URL to different database URL than HASURA_GRAPHQL_DATABASE_URL

and only by setting it to a different database URL than HASURA_GRAPHQL_DATABASE_URL it can work and migrate my hdb_catalog schema and its tables to the newest version. the other two methods resulting in error
```
{"internal":"no connection to the server\n","path":"$","error":"connection error","code":"postgres-error"}
```

This makes me have to duplicate my current hdb_catalog from the database i was using to another database. Shouldn't I be able to just use the same database as both connected database and metadata database?

### How to reproduce the issue?

1. running hasura as a container using hasura v1.3.2 image
2. try updating by changing the image used to v2.0.9 in the docker-compose.yml
3. either not set the HASURA_GRAPHQL_METADATA_DATABASE_URL env variable or set it to the same value as HASURA_GRAPHQL_DATABASE_URL env variable
4. restart the container

### Screenshots or Screencast

### Please provide any traces or logs that could help here.

### Any possible solutions?

### Can you identify the location in the source code where the problem exists?
No

### If the bug is confirmed, would you be willing to submit a PR?
No

Thanks for help

Start with the docker-compose.yml configuration and reproduce the upgrade from the v1.3.2 image to v2.0.9 using the three HASURA_GRAPHQL_METADATA_DATABASE_URL configurations described. Inspect the container startup and migration output around the reported postgres-error. Done means determining whether the same database URL is supported and fixing the migration path or documenting the required upgrade configuration.

Written by the indexing model from the issue text.