Add tracking of user actions for an action log

### Detailed Description
As a user, i want to be able to list all my relevant past actions on Basilisk. Those actions may include Buy, Sell or liquidity provisioning.

### Context
Within the UI, we want to display a list of relevant historical user actions.

### Possible Implementation

```
enum UserAction {
Buy,
Sell,
AddLiquidity,
RemoveLiquidity,
}

type BuyActionDetail {
// whatever other fields are relevant to track, just an example
balance: BigInt!
}

union UserActionDetail = BuyActionDetail

type UserAction {
ID: ID!
action: UserAction!,
detail: UserActionDetail
}
```

The issue names no files, tests, or entry points. Start by locating the action-processing and API schema entry points in the Basilisk indexer, then determine which user actions and detail fields must be stored and exposed; done means the UI can list relevant Buy, Sell, AddLiquidity, and RemoveLiquidity history.

Written by the indexing model from the issue text.