Fix various problems around projects board view (#30696)

# The problem
The previous implementation will start multiple POST requests from the
frontend when moving a column and another bug is moving the default
column will never be remembered in fact.

# What's changed

- [x] This PR will allow the default column to move to a non-first
position
- [x] And it also uses one request instead of multiple requests when
moving the columns
- [x] Use a star instead of a pin as the icon for setting the default
column action
- [x] Inserted new column will be append to the end
- [x] Fix #30701 the newly added issue will be append to the end of the
default column
- [x] Fix when deleting a column, all issues in it will be displayed
from UI but database records exist.
- [x] Add a limitation for columns in a project to 20. So the sorting
will not be overflow because it's int8.

---------

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

tests/integration/org_project_test.go

@@ -5,17 +5,17 @@ package integration
 
 import (
 	"net/http"
+	"slices"
 	"testing"
 
 	unit_model "code.gitea.io/gitea/models/unit"
+	"code.gitea.io/gitea/modules/test"
 	"code.gitea.io/gitea/tests"
 )
 
 func TestOrgProjectAccess(t *testing.T) {
 	defer tests.PrepareTestEnv(t)()
-
-	// disable repo project unit
-	unit_model.DisabledRepoUnits = []unit_model.Type{unit_model.TypeProjects}
+	defer test.MockVariableValue(&unit_model.DisabledRepoUnits, append(slices.Clone(unit_model.DisabledRepoUnits), unit_model.TypeProjects))()
 
 	// repo project, 404
 	req := NewRequest(t, "GET", "/user2/repo1/projects")