📖 Add documentation for declarative plugin

[mariuskimmina]

As discussed in #2542 I'm proposing a documentation for the declarative plugin here.
This is just a first draft an I'm open for suggestions as to what can be improved.
Also feel free to point out if anything seems incorrect.

I think the subcommands section should contain more detail but I'm unsure as to what else to say there.

[k8s-ci-robot]

Hi @mariuskimmina. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[camilamacedo86]

I loved it 🥇
Terrific work 🚀

I added a few suggetions. Also, could you please squash all commits for we are able to get it merged ?

[camilamacedo86]

I did a last round of reviews. Could you please check it out and let me know wdyt?
Also, after address, the comments could you please squash the commits for we get this one merged?

By latest, that is a terrific work 🥇

[camilamacedo86]

/ok-to-test

[mariuskimmina]

I have squashed the commits into one and have adjusted the docs according to your last review - I have slightly adjusted some of your suggestions.

[camilamacedo86]

We can test the final result by clicking on the preview test: https://deploy-preview-2562--kubebuilder.netlify.app/

The only thing that is not OK is the note, see;

By fixing that I think it is good enough for us to get merged.

[camilamacedo86]

Suggested change

	<aside class="note">
	You can check samples using this plugin by looking at the `project-<go plugin version>-addon` samples under the [testdata][testdata] directory on the root directory of the Kubebuilder project.
	</aside>
	<aside class="note">
	<h1>Examples</h1>
	You can check samples using this plugin by looking at the `project-<go plugin version>-addon` samples under the [testdata](https://github.com/kubernetes-sigs/kubebuilder/tree/master/testdata/) directory on the root directory of the Kubebuilder project.
	</aside>

Seems that the note does not work with the link alias :-(

[mariuskimmina]

That is strange, because it works in plugins.md - there an alias is also used inside the <aside> tag

[mariuskimmina]

Looking at https://deploy-preview-2562--kubebuilder.netlify.app/ the link alias works now, the problem was the usage of the code block inside the <aside> block, so I changed this section up a bit - going to squash the commits again

[camilamacedo86]

Great work 🥇
That shows good enough for us to get it merged!
However, we can always do follow-ups and etc if we see that hoes for impairments.

So,

/lgtm
/approved

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: camilamacedo86, mariuskimmina

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