Redirect /predicate/chains to Chains documentation.

[wlynch]

Changes

This sets up a redirect so for /predicate/chains to Chains documentation.

i.e. https://tekton.dev/predicate/chains/slsa/v2 -> https://github.com/tektoncd/chains/tree/main/docs/predicate/slsa/v2
(these pages don't actually exist yet).

This is a placeholder for SLSA predicate type documentation. We may try to figure out how to handle these better with the doc import process later on, but we need these to keep URL structure that AFAIK sync.py doesn't support well today. These URLs show up in Chains-generated SLSA predicates.

We do not need navigation for these URLs (we'll figure out if we want to add this later with the doc syncing).

See tektoncd/chains#906 for more details.

Fixes #561

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[wlynch]

@geriom @popcor255 ping for review 🙏 (or let me know if there's someone else I should get to review this)

[geriom]

Is there a reason for creating a _redirecs file instead of adding the redirects to netlify.toml?

Either is fine with me, just wondering if one is better than the other.

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[wlynch]

Is there a reason for creating a _redirecs file instead of adding the redirects to netlify.toml?

Nope, no particular reason. We can rewrite this in netlify.toml if we want. 🤷

[geriom]

/lgtm