Nginx plus dashboard additions

[bjee19]

Proposed changes

Problem: The Nginx Plus dashboard document needs to be updated with information on configuring access to it.

Solution: Add a section in dashboard.md giving a brief overview on how to change access to the dashboard with an example and a link to the data plane configuration document for more information. Additionally updated the api.md document to reflect the current state for NGF on main.

Testing: Checked the rendered documentation.

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[github-actions]

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[bjee19]

For the api.md file, we decided to replace the recent changes made in #120 due to those changes not reflecting the current state of NGF on main. This api.md file is a direct copy of the one currently on main.

The changes made in #120 will be merged when we merge our feature branch to main in the NGF repo.

[bjee19]

I have hereby read the F5 CLA and agree to its terms

[sjberman]

ngf team wasn't added as reviewers to this for some reason

[mjang]

Unless we're actually using these addresses, I think we're limited to the addresses in RFC 5737, "IPv4 Address Blocks Reserved for Documentation"

[bjee19]

cool, didn't know this was a thing, made the change

[mjang]

ngf team wasn't added as reviewers to this for some reason

Created #160

[mjang]

Concerns addressed