Update install instructions, making them consistent for all sub-projects

[inteon]

Goal: Reach base level of consistency for installation commands across all installation pages. Once we reach consistency, we can think about improving these instructions (keeping in mind the CRD changes coming in 1.15).

Next steps:

1. Prepare 1.15 release (drastically simplify the CRD install section & use the single fool-proof install command everywhere)

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[inteon]

Have you tested everything? No, the commands have not changed, I only expanded the flags. The only command that changed is the command that disables the approval-controller, and I copied that command from the approver-policy install page.

[inteon]

@wallrj

I updated the cert-manager instructions for approver-policy and csi-driver-spiffe (replaced helm install/ helm upgrade --install with helm upgrade --reuse-values. I also tested that this works as expected for the approver-policy installation.

[ThatsMrTalbot]

/lgtm

[inteon]

/approve

[cert-manager-prow[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: inteon

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/cert-manager/website/blob/master/OWNERS)~~ [inteon] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment