[breaking-change] Clear redirects and headers when PATCHing manifest

Without this, whenever _redirects or _headers gets PATCHed, any new values are appended to the old instead of overriding it.

src/headers.go

@@ -100,6 +100,7 @@ func ProcessHeadersFile(ctx context.Context, manifest *Manifest) error {
 	if headersEntry == nil {
 		return nil
 	}
+	manifest.Headers = []*HeaderRule{}
 
 	data, err := GetEntryContents(ctx, headersEntry)
 	if errors.Is(err, ErrNotRegularFile) {

src/redirects.go

@@ -104,6 +104,7 @@ func ProcessRedirectsFile(ctx context.Context, manifest *Manifest) error {
 	if redirectsEntry == nil {
 		return nil
 	}
+	manifest.Redirects = []*RedirectRule{}
 
 	data, err := GetEntryContents(ctx, redirectsEntry)
 	if errors.Is(err, ErrNotRegularFile) {