⚠️ deprecate declarative plugin

[camilamacedo86]

Description:

This PR deprecates the declarative plugin and adds the following notice:

Also, we are:

• Updating the docs to make clear that it is deprecated
• Removing the sample under test data to stop to block us from moving forward with upgrades, such as now that we want to bump controller runtime alpha 0.15 and it will fail in : https://prow.k8s.io/view/gs/kubernetes-jenkins/pr-logs/pull/kubernetes-sigs_kubebuilder/3394/pull-kubebuilder-test/1655479526613848064

Closes: #3186
Related to : kubernetes-sigs/kubebuilder-declarative-pattern#293

[k8s-ci-robot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[varshaprasad96]

@camilamacedo86 I'm fine moving ahead with the PR. Just want to confirm if Kubebuilder declarative pattern maintainers are comfortable with us doing this, or would like to first externalize the plugin and then deprecate (followed by remove) it. cc: @justinsb

[Kavinjsir]

LGTM 👍🏼
Nits:
What about also removing:

1. kubebuilder/docs/book/src/SUMMARY.md

   Line 122 in 7711b8f

   - [declarative/v1](./plugins/declarative-v1.md)

2. kubebuilder/docs/book/src/reference/project-config.md

   Line 87 in 7711b8f

   declarative.go.kubebuilder.io/v1:

3. kubebuilder/docs/book/src/plugins/to-be-extended.md

   Line 24 in 7711b8f

   [kubebuilder-declarative-pattern]: https://github.com/kubernetes-sigs/kubebuilder-declarative-pattern

4. kubebuilder/docs/book/src/plugins/extending-cli.md

   Line 61 in 7711b8f

   &declarativev1.Plugin{},

5. kubebuilder/pkg/cli/cli_test.go

   Line 172 in 7711b8f

   pluginChain := []string{"go.kubebuilder.io/v2", "declarative.kubebuilder.io/v1"}

[Kavinjsir]

/retest

[camilamacedo86]

/test pull-kubebuilder-e2e-k8s-1-25-3

[everettraven]

/lgtm

[Kavinjsir]

lgtm 👍🏼

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: camilamacedo86, everettraven, Kavinjsir

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