chore: adding sdk.Msg impl for ics27 MsgRegisterAccount (backport #2081)

[mergify]

This is an automatic backport of pull request #2081 done by Mergify.
Cherry-pick of 94d0840 has failed:

On branch mergify/bp/release/v5.1.x/pr-2081
Your branch is up to date with 'origin/release/v5.1.x'.

You are currently cherry-picking commit 94d0840.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	new file:   modules/apps/27-interchain-accounts/controller/types/msgs_test.go

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   modules/apps/27-interchain-accounts/controller/types/msgs.go
	both modified:   testing/values.go

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[damiannolan]

I can handle the conflicts on this. Also looks like it requires #2051 to be backported first