feat: IPEX apply, offer, agree

[iFergal]

Apply, offer, agree IPEX messages. Covers single and multi-sig as multi-sig is just a normal /ipex/* message (multi-signed) embedded in /multisig/exn.

On the recipient field:

• rp (to be renamed to ri) is all that's needed in exn messages, so recipient always specified
• no extra harm in including a.i - so I haven't removed the code that auto adds this based on the recipient field
  • once keripy has moved to rp/ri fully we can remove it from Signify.
  • for now, less likely to break things this way.

The recp field can still be removed on KERIA but that isn't needed for this PR.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.93%. Comparing base (850af59) to head (fe0dbe8).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #272      +/-   ##
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+ Coverage   83.82%   83.93%   +0.10%     
==========================================
  Files          48       48              
  Lines        4229     4257      +28     
  Branches     1034     1051      +17     
==========================================
+ Hits         3545     3573      +28     
  Misses        656      656              
  Partials       28       28              

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[lenkan]

LGTM. One thing to consider in the IpexXXXArgs interfaces is if we should be more descriptive in the property names for grant/apply/offer etc... So:

interface IpexAdmitArgs {
   grantSaid: string
]

What do you reckon?

[iFergal]

thanks, agreed @lenkan I also changed it to schemaSaid since it only works with SAIDs right now

[iFergal]

@lenkan can this be merged, or awaiting review from @rodolfomiranda? I couldn't make the dev call

[lenkan]

I think we can merge it now. No one seems to have any objections.