Add tests for installing tobs with timescale Cloud integration

[paulfantom]

What is missing?

We are not testing TimescaleCloud integration in tests.

Why do we need it?

To catch potential issues with that integration.

Anything else we need to know?:

[paulfantom]

Possible test sequence:

1. provision DB with helm chart
2. compose DBURI
3. use DBURI from previous points as an external database

[paulfantom]

Depends on https://github.com/timescale/tobs/issues/473

[nhudson]

I believe with the merge of #531 we can close this? Unless you think there is something else we need to add.