fix(cli): improve error message for invalid config (#1200)

Previously an invalid `Dioxus.toml` file would yield this error when running e.g. `dx serve`:

```
Error: Failed to load `Dioxus.toml` because: Dioxus.toml parse failed
```

This doesn't give any indication why it failed to parse. This commit updates it to include why the parsing failed, e.g.:

```
Error: Failed to load Dioxus config because: Dioxus.toml missing field `name` for key `application` at line 38 column 1
```

I initially had it format the message to include `Dioxus.toml:38:1` to be clickable in some terminals, but the location specified didn't always seem particularly relevant to the actual problem so I left it as-is.

This also fixes what I believe would be an issue on case-sensitive file systems where if `dioxus.toml` existed it would try to read `Dioxus.toml`.

I'm still fairly new to Rust, so the `.as_path()` calls may not be the best way to deal with the fact that the borrow checker wouldn't let me re-use `crate_dir` and `dioxus_conf_file`. I'm open to suggestions!

packages/cli/src/main.rs

@@ -14,7 +14,7 @@ async fn main() -> anyhow::Result<()> {
     set_up_logging();
 
     let _dioxus_config = DioxusConfig::load()
-        .map_err(|e| anyhow!("Failed to load `Dioxus.toml` because: {e}"))?
+        .map_err(|e| anyhow!("Failed to load Dioxus config because: {e}"))?
         .unwrap_or_else(|| {
             log::warn!("You appear to be creating a Dioxus project from scratch; we will use the default config");
             DioxusConfig::default()