docs: Update URLs referring to Turborepo custom remote cache server

[Naoto-Ida]

In this PR:

Hi, I noticed that in the docs, the URLs were pointing to:
https://turborepo.org/docs/features/remote-caching#custom-remote-caches

whereas now its:
https://turbo.build/repo/docs/core-concepts/remote-caching#self-hosting

Thanks for all the awesome work on this project :)

Issues reference:

• None

Checklist:

• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

• Have you lint your code with pnpm lint locally prior to submission?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you commit using Conventional Commits?

[matteovivona]

@allcontributors add @Naoto-Ida for docs

[allcontributors]

@matteovivona

I've put up a pull request to add @Naoto-Ida! 🎉

[matteovivona]

🎉 This PR is included in version 2.0.9 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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