prepare changelog for 3.1.5 (#6049)

Author: randmonkey

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.
 --->
+ - [3.1.5](#315)
  - [3.1.4](#314)
  - [3.1.3](#313)
  - [3.1.2](#312)
@@ -86,7 +87,9 @@ Adding a new version? You'll need three changes:
  - [0.0.5](#005)
  - [0.0.4 and prior](#004-and-prior)
 
-## Unreleased
+## [3.1.5]
+
+ Release date: 2024-05-17
 
 ### Fixed
 
@@ -3357,6 +3360,7 @@ Please read the changelog and test in your environment.
  - The initial versions  were rapildy iterated to deliver
    a working ingress controller.
 
+[3.1.5]: https://github.com/kong/kubernetes-ingress-controller/compare/v3.1.4...v3.1.5
 [3.1.4]: https://github.com/kong/kubernetes-ingress-controller/compare/v3.1.3...v3.1.4
 [3.1.3]: https://github.com/kong/kubernetes-ingress-controller/compare/v3.1.2...v3.1.3
 [3.1.2]: https://github.com/kong/kubernetes-ingress-controller/compare/v3.1.1...v3.1.2