[OpenID-Specs-eKYC-IDA] Issue #1330: Suggest that there be a default for "attachments_supported" (openid/ekyc-ida)

[mhainework]

New issue 1330: Suggest that there be a default for "attachments_supported"
https://bitbucket.org/openid/ekyc-ida/issues/1330/suggest-that-there-be-a-default-for

Mark Haine:

`attachments_supported`: REQUIRED when OP supports attachments. JSON array containing all attachment types supported by the OP. Possible values are `external` and `embedded`. When present this array MUST have at least one member.