[k8s] [config] merge initContainers by name

[SeungjinYang]

Currently, if the same initContainers field is specified on both client and server, the merged initContainers field ends up containing duplicate values and job launch would fail.

`initContainers` user merge strategy with a mergeKey of `name` according to https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.30/

We actually already have a logic for dealing with list merges with a mergekey of name - so I just use that.

I am starting to have a bigger question of how much longer we want to be maintaining this custom merge logic for kubernetes, but for now, this works and will solve some immediate user pains.

Tested (run the relevant ones):

• Code formatting: install pre-commit (auto-check on commit) or bash format.sh
• Manual test: specify the same initContainers on both client and server and verify no duplicate is created after config merge.

[romilbhardwaj]

Looks like the name key in init containers is required. Can we dedup the merged list based on name?

[SeungjinYang]

reference for myself:
https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.30/
tl;dr chatGPT seems to have lied, initContainers does use merge with merge key of name

edit: also we already have a way to handle this case, so I'm just going to freeload off of that

[cg505]

can we add a test?