push sigstore attestation on Maven Central as part of release script

[monperrus]

• push sigstore to Maven central as part as release pipeline
• push sigstore attestation on Maven Central as part of CD
• document how to do this on a new post on the Chains website.

ref: https://www.sonatype.com/blog/central-publisher-portal-now-validates-sigstore-signatures

[LogFlames]

Autoclosed by PR, not yet documented on CHAINS website.