feat: Add the possibility to update the default handler for the Global Resource Property Registry

[shlomodaari]

• feat: Add possibility to re-set default handler for Global Resource Property Registry.

• feat: Add not null check for defaultHandler param.

[dbyron-sf]

This definitely needs tests, but also motivation for why we need/want this.

[shlomodaari]

@dbyron-sf This is part of a code that was backported to 1.28 1.29 1.30 but was missed in 1.31 and you approved it last year tbh.
https://github.com/spinnaker/clouddriver/blob/release-1.29.x/clouddriver-kubernetes/src/main/java/com/netflix/spinnaker/clouddriver/kubernetes/description/GlobalResourcePropertyRegistry.java
https://github.com/spinnaker/clouddriver/blob/release-1.30.x/clouddriver-kubernetes/src/main/java/com/netflix/spinnaker/clouddriver/kubernetes/description/GlobalResourcePropertyRegistry.java
https://github.com/spinnaker/clouddriver/blob/release-1.32.x/clouddriver-kubernetes/src/main/java/com/netflix/spinnaker/clouddriver/kubernetes/description/GlobalResourcePropertyRegistry.java

Let me know if you have any additional questions please

[shlomodaari]

Can be closed now we found the missing backport :)

[edgarulg]

mergify never created the backport for 1.31.x: #6323