Refactor htmx and fetch-action related code (#37186)

This is the first step (the hardest part):

* repo file list last commit message lazy load
* admin server status monitor
* watch/unwatch (normal page, watchers page)
* star/unstar (normal page, watchers page)
* project view, delete column
* workflow dispatch, switch the branch
* commit page: load branches and tags referencing this commit

The legacy "data-redirect" attribute is removed, it only makes the page
reload (sometimes using an incorrect link).

Also did cleanup for some devtest pages.

services/context/base_test.go

@@ -38,9 +38,10 @@ func TestRedirect(t *testing.T) {
 
 	req, _ = http.NewRequest(http.MethodGet, "/", nil)
 	resp := httptest.NewRecorder()
-	req.Header.Add("HX-Request", "true")
+	req.Header.Add("X-Gitea-Fetch-Action", "1")
 	b := NewBaseContextForTest(resp, req)
 	b.Redirect("/other")
-	assert.Equal(t, "/other", resp.Header().Get("HX-Redirect"))
-	assert.Equal(t, http.StatusNoContent, resp.Code)
+	assert.Contains(t, resp.Header().Get("Content-Type"), "application/json")
+	assert.JSONEq(t, `{"redirect":"/other"}`, resp.Body.String())
+	assert.Equal(t, http.StatusOK, resp.Code)
 }