Update localhost refs

[LDiazN]

Update all clickhouse localhost refs in backend to use a configuration parameter instead.

It's set up such that if no such configuration is provided, it defaults to the old behaviour of having localhost hardcoded

The following config file requires an update:

analysis.conf

# Managed by ansible, see roles/ooni-backend/tasks/main.yml
# [s3bucket]
# bucket_name = ooni-data-eu-fra-test
# aws_access_key_id =
# aws_secret_access_key =

[backup]
# space separated
table_names = citizenlab fastpath jsonl

# New
[DB]
uri = clickhouse url here

Closes #954

Related to ooni/devops#242

[hellais]

Only support setting db-uri using CLI flag

[hellais]

I would suggest dropping all this config file handling stuff and only allow setting db-uri via the CLI flag --db-uri.

[hellais]

The reason is that we are potentially adding some extra code paths that can be tricky to debug if something is not working as intended.

[LDiazN]

How do we set up the flag --db-uri when deployed? I originally used the conf file because it's where we specify configurations in Ansible