Amend GetTimestampAtHeight to accept ConnectionI interface

[DimitrisJim]

Summary

The connectionKeeper's GetTimestampAtHeight method currently expects a ConnectionEnd type. This is in contrast to the rest of the methods which are defined based on the ConnectionI interface defined in exported.

This results in a requirement to mix calls (see #3840) to access connection keeper methods since channelKeeper.GetConnection returns the interface when GetTimestampAtHeight requires the type (which is accessed via connectionKeeper.GetConnection).

Proposal

Change GetTimestampAtHeight's sig to accept the interface instead of the type.

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[DimitrisJim]

note: unsure if there's history behind this? Also, pretty sure this is API-breaking, though I wouldn't expect anyone to actually be using it.

[crodriguezvega]

Good catch, @DimitrisJim! it could be that maybe this is even not API breaking? The ConnectionEnd fully implements the ConnectionI interface, so maybe it's possible to just replace the argument type without any harm.

[DimitrisJim]

due to it being a public symbol it will necessarily be API-breaking I'd assume. People do wild shit with code. I do agree that yeah, call sites won't be affected due to the ConnectionEnd implementing that interface, on our end this just changes signatures.

[DimitrisJim]

Closing, this mixed usage should now not be an issue considering we removed that interface #5770