prepare release 3.1.2: update CHANGELOG for kic 3.1.2 (#5694) (#5696)

* update CHANGELOG for kic 3.1.2

* update CHANGELOG: add link and compare link

(cherry picked from commit 57d7b17)

Co-authored-by: Tao Yi <tao.yi@konghq.com>

CHANGELOG.md

@@ -7,6 +7,7 @@ Adding a new version? You'll need three changes:
 * Add the diff link, like "[2.7.0]: https://github.com/kong/kubernetes-ingress-controller/compare/v1.2.2...v1.2.3".
   This is all the way at the bottom. It's the thing we always forget.
 --->
+ - [3.1.2](#312)
  - [3.1.1](#311)
  - [3.1.0](#310)
  - [3.0.2](#302)
@@ -83,7 +84,9 @@ Adding a new version? You'll need three changes:
  - [0.0.5](#005)
  - [0.0.4 and prior](#004-and-prior)
 
-## Unreleased
+## [3.1.2]
+
+> Release date: 2024-03-08
 
 ### Fixed
 
@@ -93,6 +96,8 @@ Adding a new version? You'll need three changes:
 
 ## [3.1.1]
 
+> Release date: 2024-02-29
+
 ### Added
 
 - Managed `Gateway`s now get reconciled by the `Gateway` controller, but do not
@@ -3295,6 +3300,7 @@ Please read the changelog and test in your environment.
  - The initial versions  were rapildy iterated to deliver
    a working ingress controller.
 
+[3.1.2]: https://github.com/kong/kubernetes-ingress-controller/compare/v3.1.1...v3.1.2
 [3.1.1]: https://github.com/kong/kubernetes-ingress-controller/compare/v3.1.0...v3.1.1
 [3.1.0]: https://github.com/kong/kubernetes-ingress-controller/compare/v3.0.2...v3.1.0
 [3.0.2]: https://github.com/kong/kubernetes-ingress-controller/compare/v3.0.1...v3.0.2