Explain how to install cert-manager using ArgoCD

[wallrj]

Preview: https://deploy-preview-1447--cert-manager-website.netlify.app/docs/installation/continuous-deployment-and-gitops/#using-argocd

Continuing the work @shahkv95 started in #1350

• cert-manager installation using argocd #1350

Some months later, in #1350 (comment) @Tokynet wrote:

@wallrj this is not my code/fix BUT i'm currently affected by this.
I will pull this branch and make the suggested edits after my comments below are accepted or better suggestions are made.

So, in response to that, I've created this PR in which I've implemented the changes that I suggested in #1350 (review) and rebased on top of latest origin/master.

@Tokynet Please either review and make suggestions in thie PR, or branch from wallrj:cert-manager-argocd and continue the work on your own branch, create your own PR and then ping me for

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[inteon]

NOTE: This still has to be verified

Normally by using ServerSideApply and ServerSide diffing, there should be no issues with mutating webhooks:

Suggested change

	```yaml
	# application.yaml
	apiVersion: argoproj.io/v1alpha1
	kind: Application
	metadata:
	name: cert-manager
	namespace: argocd
	annotations:
	argocd.argoproj.io/sync-options: SkipDryRunOnMissingResource=true
	finalizers:
	- resources-finalizer.argocd.argoproj.io
	spec:
	destination:
	namespace: cert-manager
	server: https://kubernetes.default.svc
	project: default
	source:
	chart: cert-manager
	repoURL: https://charts.jetstack.io
	targetRevision: [[VAR::cert_manager_latest_version]]
	helm:
	values: |
	installCRDs: true
	syncPolicy:
	automated:
	prune: true
	selfHeal: true
	syncOptions:
	- CreateNamespace=true
	```yaml
	# application.yaml
	apiVersion: argoproj.io/v1alpha1
	kind: Application
	metadata:
	name: cert-manager
	namespace: argocd
	annotations:
	argocd.argoproj.io/compare-options: ServerSideDiff=true
	finalizers:
	- resources-finalizer.argocd.argoproj.io
	spec:
	destination:
	namespace: cert-manager
	server: https://kubernetes.default.svc
	project: default
	source:
	chart: cert-manager
	repoURL: https://charts.jetstack.io
	targetRevision: [[VAR::cert_manager_latest_version]]
	helm:
	values: |
	installCRDs: true
	syncPolicy:
	automated:
	prune: true
	selfHeal: true
	syncOptions:
	- CreateNamespace=true
	- ServerSideApply=true

This change is based on https://argo-cd.readthedocs.io/en/stable/user-guide/diff-strategies/ and https://argo-cd.readthedocs.io/en/stable/user-guide/sync-options/#server-side-apply.