cln-bip353: add plugin that fetches payment instructions from human readable addresses

[daywalker90]

Changelog-Add: new plugin cln-bip353 that can fetch bolt12 offers from human readable addresses

Important

25.09 FREEZE July 28TH: Non-bugfix PRs not ready by this date will wait for 25.12.

RC1 is scheduled on August 11th

The final release is scheduled for September 1st.

Adds a new rpc command fetchbip353 [address] that fetches payment instructions from a bip-353 address and returns an object containing:

• offer: the encoded bolt12 offer string
• proof: lowercase hex encoded proof
• description: optional description from the payee
• amount_msat: optional amount in msat for fixed amount offers

Fixes: #8361

Checklist

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• The changelog has been updated in the relevant commit(s) according to the guidelines.
• Tests have been added or modified to reflect the changes.
• Documentation has been reviewed and updated as needed.
• Related issues have been listed and linked, including any that this PR closes.