chore: add potential use cases documentation for ica (#2594) (#2663)

## Description

will fix ordering after #2561 is merged, so review that first

closes: #2472

---

Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

- [ ] Targeted PR against correct branch (see [CONTRIBUTING.md](https://github.com/cosmos/ibc-go/blob/master/CONTRIBUTING.md#pr-targeting))
- [ ] Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
- [ ] Code follows the [module structure standards](https://github.com/cosmos/cosmos-sdk/blob/main/docs/docs/building-modules/10-structure.md).
- [ ] Wrote unit and integration [tests](https://github.com/cosmos/ibc-go/blob/master/CONTRIBUTING.md#testing)
- [ ] Updated relevant documentation (`docs/`) or specification (`x/<module>/spec/`)
- [ ] Added relevant `godoc` [comments](https://blog.golang.org/godoc-documenting-go-code).
- [ ] Added a relevant changelog entry to the `Unreleased` section in `CHANGELOG.md`
- [ ] Re-reviewed `Files changed` in the Github PR explorer
- [ ] Review `Codecov Report` in the comment section below once CI passes

(cherry picked from commit 7190305)

Co-authored-by: colin axnér <[email protected]>

docs/.vuepress/config.js

@@ -193,6 +193,11 @@ module.exports = {
                   directory: false,
                   path: "/apps/interchain-accounts/parameters.html",
                 },
+                {
+                  title: "Development Use Cases",
+                  directory: false,
+                  path: "/apps/interchain-accounts/development.html",
+                },
                 {
                   title: "Active Channels",
                   directory: false,

docs/apps/interchain-accounts/active-channels.md

@@ -1,5 +1,5 @@
 <!--
-order: 5
+order: 6
 -->
 
 # Understanding Active Channels 
@@ -29,4 +29,4 @@ The following is a list of issues which will provide the infrastructure to make
 - [IBC Channel Upgrades](https://github.com/cosmos/ibc-go/issues/1599)
 - [Implement ORDERED_ALLOW_TIMEOUT logic in 04-channel](https://github.com/cosmos/ibc-go/issues/1661)
 - [Add ORDERED_ALLOW_TIMEOUT as supported ordering in 03-connection](https://github.com/cosmos/ibc-go/issues/1662)
-- [Allow ICA channels to be opened as ORDERED_ALLOW_TIMEOUT](https://github.com/cosmos/ibc-go/issues/1663)
+- [Allow ICA channels to be opened as ORDERED_ALLOW_TIMEOUT](https://github.com/cosmos/ibc-go/issues/1663)

docs/apps/interchain-accounts/auth-modules.md

@@ -1,5 +1,5 @@
 <!--
-order: 6
+order: 7
 -->
 
 # Building an authentication module

docs/apps/interchain-accounts/development.md

@@ -0,0 +1,36 @@
+<!--
+order: 5
+-->
+
+# Development use cases
+
+The initial version of interchain accounts allowed for the controller module to be extended by providing it with an underlying application which would handle all packet callbacks.
+That functionality is now being deprecated in favor of alternative approaches. 
+This document will outline potential use cases and redirect each use case to the appropriate documentation. 
+
+## Custom authentication 
+
+Interchain accounts may be associated with alternative types of authentication relative to the traditional public/private key signing. 
+If you wish to develop or use interchain accounts with a custom authentication module, we recommend you use ibc-go v6 or greater. 
+
+The custom authentication module should interact with the controller module via the [MsgServer](./messages.md).
+
+## Redirection to a smart contract
+
+It may be desirable to allow smart contracts to control an interchain account.
+To faciliate such an action, the controller module may be provided an underlying application which redirects to smart contract callers. 
+An improved design has been suggested in [ADR 008](https://github.com/cosmos/ibc-go/pull/1976) which performs this action via middleware. 
+
+Implementors of this use case are recommended to follow the ADR 008 approach.
+The underlying application may continue to be used as a short term solution for ADR 008 and the [legacy API](./auth-modules.md#registerinterchainaccount) should continue to be utilized in such situations. 
+
+## Packet callbacks
+
+If a developer requires access to packet callbacks for their use case, then they having the following options:
+
+1. Write a smart contract which is connected via an ADR 008 or equivalent IBC application (recommended).
+2. Use the controller's underlying application to implement packet callback logic.
+
+If the first case, the smart contract should use the [MsgServer](./messages.md).
+
+In the second case, the underlying application should use the [legacy API](./auth-modules.md#registerinterchainaccount).