Fix channel identifier format to be compatible with IBC-go

[adizere]

Summary of Bug

In the modules, we define a channel id to be represented as a u64.

https://github.com/informalsystems/ibc-rs/blob/baf0e3f60f37934cab89526f47f7cb6524f7d92c/modules/src/core/ics24_host/identifier.rs#L339

The code performs additional validation and requires channel IDs in received messages to have exactly the channel-N format. This is not part of the IBC specification. Instead, channel identifiers should be validated as follows:

• should contain alphanumeric chars and
• should have a certain maximum length.

This problem only exists for channel IDs. Client and connection ID validation conforms with the IBC spec.

Version

v0.15

Acceptance Criteria

• Channel identifiers no longer restrict the format to u64 based representation.
• Hermes has no assumptions on the format of channel identifiers aside from the validation rules described above.

---

For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate milestone (priority) applied
• Appropriate contributors tagged
• Contributor assigned/self-assigned

[ancazamfir]

I think we should fix this in v1. I believe it also affects the relayer, if a chain uses something else than channel-n hermes will not relay for it.

[adizere]

I think we should fix this in v1. I believe it also affects the relayer, if a chain uses something else than channel-n hermes will not relay for it.

Managed to confirm this:

$ hermes query channel end ibc-0 transfer chan-2
    Finished dev [unoptimized + debuginfo] target(s) in 0.26s
     Running `target/debug/hermes query channel end ibc-0 transfer chan-2`
error: Invalid value "chan-2" for '<CHANNEL_ID>': channel identifiers are expected to be in `channel-{N}` format