feat(argo-cd): Allow configuring Dex's init image resources separately

[Angelin01]

Motivation:

The dex server, when running, can use as little as 1m CPU and 38Mi of memory:

> kubectl -n argocd top pod argo-cd-argocd-dex-server-549f5d748c-q8fmq
NAME                                         CPU(cores)   MEMORY(bytes)   
argo-cd-argocd-dex-server-549f5d748c-q8fmq   1m           38Mi            

However, using a low resource spec to match said usage, the init container can crash with an OOMKilled, leading to crashloopbackoffs from Dex:

argo-cd-argocd-dex-server-99794466c-d7zvr                   0/1     Init:OOMKilled      0                12s

Configuring the resources separately allows us to avoid the OOMKilled but also not overcommit resources to the long-running Dex server. I've made the change backwards compatible: it will fallback to Dex's resources in case the init container's are not configured.

One note: I've put the resources inside the initImage key, however I don't know if it's appropriate. I failed to find a better location though.

Checklist:

• I have bumped the chart version according to versioning
• I have updated the documentation according to documentation
• I have updated the chart changelog with all the changes that come with this pull request according to changelog.
• Any new values are backwards compatible and/or have sensible default.
• I have signed off all my commits as required by DCO.
• My build is green (troubleshooting builds).

[yu-croco]

LGTM