common: initial database handling

Can be configured from the config file, and also using environment
options.

```toml
[database]
url = "postgresql://fc_ci:password@localhost/fc_ci"
max_connections = 20
min_connections = 5
connect_timeout = 30
idle_timeout = 600
max_lifetime = 1800
```

We'll want to support SQlite in the future, and better secret handling
for database credentials. For now, this is workable.

---

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I36b4c1306511052a2748ca9d5d3429366a6a6964

crates/common/src/lib.rs

@@ -1,10 +1,17 @@
 //! Common types and utilities for CI
 
+pub mod config;
+pub mod database;
 pub mod error;
 pub mod migrate;
 pub mod migrate_cli;
 pub mod models;
 
+#[cfg(test)]
+mod tests;
+
+pub use config::*;
+pub use database::*;
 pub use error::*;
 pub use migrate::*;
 pub use models::*;