fix!: allow safe leverage operations during partial oracle outages (backport #1821)

[mergify]

This is an automatic backport of pull request #1821 done by Mergify.
Cherry-pick of 87b9ed4 has failed:

On branch mergify/bp/release/v4.1.x/pr-1821
Your branch is up to date with 'origin/release/v4.1.x'.

You are currently cherry-picking commit 87b9ed4.
  (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:
	modified:   CHANGELOG.md
	modified:   x/leverage/client/tests/tests.go
	modified:   x/leverage/keeper/borrows.go
	modified:   x/leverage/keeper/collateral.go
	new file:   x/leverage/keeper/errors.go
	new file:   x/leverage/keeper/errors_test.go
	modified:   x/leverage/keeper/grpc_query.go
	modified:   x/leverage/keeper/grpc_query_test.go
	modified:   x/leverage/keeper/iter.go
	modified:   x/leverage/keeper/keeper.go
	modified:   x/leverage/keeper/limits.go
	modified:   x/leverage/keeper/liquidate.go
	modified:   x/leverage/keeper/msg_server.go
	modified:   x/leverage/keeper/oracle.go
	modified:   x/leverage/keeper/oracle_test.go
	new file:   x/leverage/keeper/outage_test.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   proto/umee/leverage/v1/query.proto
	both modified:   swagger/swagger.yaml
	both modified:   x/leverage/types/query.pb.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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