Update IBC events docs and code (#6798)

* update msgs type from opaque

* update spec for createclient

* update events spec for handshake cals

* update packet events for spec and code

* add relayer events doc

* update ibc-transfer events

* fix build

* small fix from self review

* update channel msgs types

* acknowledgement_packet -> acknowledge_packet

* Apply suggestions from code review

Co-authored-by: Federico Kunze <31522760+fedekunze@users.noreply.github.com>

* fix spec issues for ibc and ibc-transfer

* add golang relayer link

Co-authored-by: Federico Kunze <31522760+fedekunze@users.noreply.github.com>

docs/ibc/README.md

@@ -1,7 +1,7 @@
 <!--
 order: false
 parent:
-  order: 4
+  order: 5
 -->
 
 # IBC
@@ -11,6 +11,7 @@ This repository contains reference documentation for the IBC protocol integratio
 1. [Overview](./overview.md)
 2. [Integration](./integration.md)
 3. [Customization](./custom.md)
+4. [Relayer](./relayer.md)
 
 After reading about IBC, head on to the [Building Modules
 documentation](../building-modules/README.md) to learn more about the process of building modules.

docs/ibc/relayer.md

@@ -0,0 +1,45 @@
+<!--
+order: 4
+-->
+
+# Relayer
+
+## Pre-requisites Readings
+
+- [IBC Overview](./overview.md) {prereq}
+- [Events](../core/events.md) {prereq}
+
+## Events
+
+Events are emitted for every transaction processed by the base application to indicate the execution
+of some logic clients may want to be aware of. This is extremely useful when relaying IBC packets.
+Any message that uses IBC will emit events for the corresponding TAO logic executed as defined in
+the [IBC events spec](https://github.com/cosmos/cosmos-sdk/tree/master/x/ibc/spec/06_events.md).
+
+In the SDK, it can be assumed that for every message there is an event emitted with the type `message`,
+attribute key `action`, and an attribute value representing the type of message sent 
+(`channel_open_init` would be the attribute value for `MsgChannelOpenInit`). If a relayer queries 
+for transaction events, it can split message events using this event Type/Attribute Key pair.
+
+The Event Type `message` with the Attribute Key `module` may be emitted multiple times for a single
+message due to application callbacks. It can be assumed that any TAO logic executed will result in 
+a module event emission with the attribute value `ibc_<submodulename>` (02-client emits `ibc_client`).
+
+### Subscribing with Tendermint 
+
+Calling the Tendermint RPC method `Subscribe` via [Tendermint's Websocket](https://docs.tendermint.com/master/rpc/) will return events using
+Tendermint's internal representation of them. Instead of receiving back a list of events as they
+were emitted, Tendermint will return the type `map[string][]string` which maps a string in the
+form `<event_type>.<attribute_key>` to `attribute_value`. This causes extraction of the event 
+ordering to be non-trivial, but still possible.
+
+A relayer should use the `message.action` key to extract the number of messages in the transaction
+and the type of IBC transactions sent. For every IBC transaction within the string array for
+`message.action`, the necessary information should be extracted from the other event fields. If
+`send_packet` appears at index 2 in the value for `message.action`, a relayer will need to use the
+value at index 2 of the key `send_packet.packet_sequence`. This process should be repeated for each
+piece of information needed to relay a packet.
+
+## Example Implementations
+
+- [Golang Relayer](https://github.com/iqlusioninc/relayer)