feat: Clarify NIC install & upgrade steps

[ADubhlaoich]

Proposed changes

This commit makes a number of changes to clarify what the precise steps are to install, upgrade and uninstall NGINX Ingress Controller

• The Install document clarifies necessary steps
• Uninstall steps have been moved to the bottom of the document
• Upgrade instructions have been moved into their own document

The changes made focused on clarifying the critical path for one single user story, as lots of unnecessary contextual information was being provided, which was causing confusion.

With this commit, the general reading and execution flow for these deployment steps become more coherent. Similar changes may be made for Manifests documentation, if common steps are identified.

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• If the change involves potentially sensitive changes¹, I have assessed the possible impact
• If applicable, I have added tests that prove my fix is effective or that my feature works
• I have ensured that existing tests pass after adding my changes
• If applicable, I have updated README.md

Footnotes

1. Potentially sensitive changes include anything involving code, personally identify information (PII), live URLs or significant amounts of new or revised documentation. Please refer to our style guide for guidance about placeholder content. ↩

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[pdabelf5]

The OCI example above uses --set arguments to pass the correct values to the helm command. We should be consistent. Also, the command does not describe what configuration should be included in the values file.

[ADubhlaoich]

@pdabelf5 In terms of consistency, would it be preferable to use --set arguments or the file?

My gut instinct is that the arguments could be faster for a user in terms of being able to easily copy & paste a single command, in comparison to editing a file.

[ADubhlaoich]

From an internal conversation with @pdabelf5, we've decided going forward that the instructions should include both working with certificate files and JWTs as tabs akin to what NGINX Plus's instructions do.

JWT is the newer convention so will be presented first: overall this will make both the image documents more consistent in their layouts, as well as consistent across NGINX documentation.