feat: add a container indicator (#3304)

* test: add mock method for absolute files

Signed-off-by: Harald Hoyer <harald@hoyer.xyz>

* feat(module): add a container indicator module

Adds a container type indicator, if inside a container,
detected via the presence of some marker files.

E.g. inside a podman container entered with `toolbox enter`
the prompt changes to the container name and version.

```
starship on  container_rebased [$!] is 📦 v1.0.0 via 🦀 v1.56.1
❯ toolbox enter

starship on  container_rebased [$!] is 📦 v1.0.0 via 🦀 v1.56.1
⬢ [fedora-toolbox:35] ❯
```

Signed-off-by: Harald Hoyer <harald@hoyer.xyz>

src/configs/mod.rs

@@ -11,6 +11,7 @@ pub mod cmake;
 pub mod cmd_duration;
 pub mod cobol;
 pub mod conda;
+pub mod container;
 pub mod crystal;
 pub mod custom;
 pub mod dart;
@@ -93,6 +94,7 @@ pub struct FullConfig<'a> {
     cmd_duration: cmd_duration::CmdDurationConfig<'a>,
     cobol: cobol::CobolConfig<'a>,
     conda: conda::CondaConfig<'a>,
+    container: container::ContainerConfig<'a>,
     crystal: crystal::CrystalConfig<'a>,
     dart: dart::DartConfig<'a>,
     deno: deno::DenoConfig<'a>,
@@ -172,6 +174,7 @@ impl<'a> Default for FullConfig<'a> {
             cmd_duration: Default::default(),
             cobol: Default::default(),
             conda: Default::default(),
+            container: Default::default(),
             crystal: Default::default(),
             dart: Default::default(),
             deno: Default::default(),