Add blog post: Artifact Storage in Tekton Chains

[ngelman1]

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This PR adds a new blog post titled "Artifact Storage in Tekton Chains".
The post provides a comprehensive overview of the supported storage backends for Tekton Chains, including Tekton (annotations), OCI, GCS, DocDB, Grafeas, Archivista, and PubSub.
It details how each backend organizes and persists signatures and attestations, along with the necessary configuration keys.
This guide aims to help users select and configure the storage solution that best fits their infrastructure needs.

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[waveywaves]

Hi Naomi ! Thank you for opening this. Currently the suggested blogpost looks more like documentation. Could we start with and Introduction first where we also introduce a problem statement or a scenario or show why would we like to talk about the storage backends in this blogpost, then we can segue into how we solve the problem in chains and then a CTA to check out chains and link it to a demo or tutorial https://killercoda.com/tekton/course/supply-chain-security