cli: remove the 'Caused by' section in the error message

[soupi]

What

https://hasurahq.atlassian.net/browse/V3DX-1053

Before:

$ CONNECTION_URI="postgresql://re" cargo run --bin ndc-postgres-cli -- --context='/tmp/baba' update
Error: error communicating with database: failed to lookup address information: Name or service not known

Caused by:
    failed to lookup address information: Name or service not known

After:

$ CONNECTION_URI="postgresql://re" cargo run --bin ndc-postgres-cli -- --context='/tmp/baba' update
ERROR: error communicating with database: failed to lookup address information: Name or service not known

How

Instead of having a main() -> anyhow::Result<()>, we explicitly handle printing the error.
https://docs.rs/anyhow/1.0.69/anyhow/struct.Error.html#display-representations