[skip ci] add path filters to workflows

Signed-off-by: ngn <ngn@ngn.tf>

.gitea/workflows/build-api.yml

@@ -3,6 +3,7 @@ name: Build the docker image for the API
 on:
   push:
     branches: ["main"]
+    paths: ["api/**"]
 
 env:
   REGISTRY: git.ngn.tf

.gitea/workflows/build-app.yml

@@ -3,6 +3,7 @@ name: Build the docker image for the frontend application
 on:
   push:
     branches: ["main"]
+    paths: ["app/**"]
 
 env:
   REGISTRY: git.ngn.tf

.gitea/workflows/build-doc.yml

@@ -3,6 +3,7 @@ name: Build the docker image for the doc server
 on:
   push:
     branches: ["main"]
+    paths: ["doc/**"]
 
 env:
   REGISTRY: git.ngn.tf