refactor(environment): rename config keys to camelCase

Aligns environment.* shape with TypeScript convention.
Renames: api_url -> apiBaseUrl, api_key -> apiKey,
use_api_key -> useApiKey, refresh_interval -> refreshInterval,
google_map_api_key -> googleMapApiKey.

The local environment.{ts,development.ts,local.ts} files are
gitignored and have already been migrated; this commit updates
the tracked example file and the only consumer (apiInterceptor).

src/app/core/interceptors/api.interceptor.ts

@@ -7,7 +7,7 @@ export const apiInterceptor: HttpInterceptorFn = (req, next) => {
         setHeaders: {
             ...({ 'Content-Type': 'application/json', 'Accept': 'application/json' }),
         },
-        url: `${environment.api_url}${req.url}`
+        url: `${environment.apiBaseUrl}${req.url}`
     });
     return next(apiReq);
 };