feat: Add vale rule to block use of site in local partials

[nfrankel]

Content Description

Add vale rule to block use of site in local partials. Also fix existing partials to conform to the rule.

Didn't fix usage of fragments because there were too many existing violations.

We want to avoid using @site directive to reference docs specific _partials (references inside vcluster, platform or versioned folders).

To make this check automated, we would like to a create a vale rule to capture and enforce the logic.

Preview link

https://deploy-preview-425--vcluster-docs-site.netlify.app/docs/

Internal Reference

Closes DOC-287

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[Piotr1215]

We should also add the same rule for the _fragments folders, as they are used with partials.

@site calls should be allowed for the docs folder in the repo root (which should already be ok with the rule):

.
├── get-started.mdx
├── index.mdx
└── _partials
    ├── kubeconfig_update.mdx
    └── managed_k8s_install_vcluster.mdx

1 directory, 4 files

It's good to test the rule in the vale studio and provide a sharable test result link in the PR.

[Piotr1215]

Thank you for the PR @nfrankel.

Adding vale studio tests: https://studio.vale.sh/s/f028e90494c82779de89c8acf28de041