Break down the cloud script

At the moment `cloud` - our cloud deployment management script is 2099 lines long. That's too much, especially for bash code. Split the file into modules, e.g. `psql.sh`, `bigquery.sh`, `password.sh`, `secret.sh`, and so on. Use the double-include guard and module include logic from [thud](https://github.com/spbnick/thud/), but still expect to be executed from the source directory.

Start by reading the 2099-line `cloud` script and the double-include guard and module include logic in thud. Identify the cloud-provider and credential-related sections for modules such as `psql.sh`, `bigquery.sh`, `password.sh`, and `secret.sh`; done means the script is split into modules while still executing from the source directory.

Written by the indexing model from the issue text.