fix: Anoncreds Offer Attachment Type

[gmulhearn]

issue-credential-v2 anoncreds didcomm attachments are sending with anoncreds/[email protected] format type rather than anoncreds/[email protected]

spec:
https://github.com/hyperledger/aries-rfcs/blob/main/features/0771-anoncreds-attachments/README.md#credential-offer-format

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[TimoGlastra]

I wanted to make sure this won't break previous versions, but we basically allow any of the identifiers for all messags, which is a bit weird but in this case helps a lot (but probably also why we didn't dettect this for so long)

[gmulhearn]

yep makes sense. i'm not sure if you guys had been interop testing with acapy, but they also have some minor issues with the attachment naming which i imagine would cause interop issues (see openwallet-foundation/acapy#3374). Hopefully after that we can have some good interop. this is specifically coming up as i've been testing out cheqd anoncreds (being introduced to acapy soon).