fix(notifications): Include ClusterRole manifests in cluster-wide installation

[motoki317]

Fixes #16022 (along with #16057)
Related: argoproj/argo-helm#2315

I have added a ClusterRole and a ClusterRoleBinding manifests to the cluster-wide installation manifests, and regenerated install.yaml and ha/install.yaml with make manifests.

This PR also includes:

• A small refactoring to controller's code which improves readability (that I have noticed by reading fix(notifications): Allow notifications controller to notify on all namespaces #15702)
• An update to Applications in any namespace docs to take into account the new notifications-controller feature introduced by fix(notifications): Allow notifications controller to notify on all namespaces #15702.

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
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[motoki317]

I commented in #16022 (comment), but now I'm not sure if we need this PR or not.
Adapt Kubernetes RBAC part in documentation already states that users need to apply extra manifests in examples/k8s-rbac/argocd-server-applications if they want to use Applications in any namespace.
But I think this part of documentation is easy to miss. Maybe we can make the extra manifests part of the default installation manifests, like I did in this change?

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (48f175b) 49.56% compared to head (e5dec6e) 49.55%.
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #16153      +/-   ##
==========================================
- Coverage   49.56%   49.55%   -0.02%     
==========================================
  Files         269      269              
  Lines       46827    46891      +64     
==========================================
+ Hits        23212    23236      +24     
- Misses      21339    21374      +35     
- Partials     2276     2281       +5     

Files	Coverage Δ
notification_controller/controller/controller.go	62.93% <50.00%> (ø)

... and 6 files with indirect coverage changes

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[motoki317]

Maybe we can make the extra manifests part of the default installation manifests, like I did in this change?

@crenshaw-dev @mayzhang2000 It would be awesome if you had opinions to my comment above, or to whether we need this PR at all or not.
Thanks!

[motoki317]

Closing this PR as the cluster roles should still be an opt-in: #16022 (comment)