feat(docs): add Foundry guides for Payment and JsonApi (#568)

Author: dineshpinto

docs/fdc/attestation-types/json-api.mdx

@@ -0,0 +1,42 @@
+---
+title: JsonApi
+description: An attestation request that fetches data from the given url and then edits the information with a jq transformation.
+keywords: [fdc, oracle, flare-data-connector, flare-network]
+sidebar_position: 1
+---
+
+An attestation request that fetches data from the given url and then edits the information with a jq transformation.
+
+## Supported sources
+
+- `WEB2`
+- test networks: `testWEB2`
+
+## Request
+
+| Field           | Solidity type | Description                                              |
+| --------------- | ------------- | -------------------------------------------------------- |
+| `url`           | `string`      | URL of the data source.                                  |
+| `postprocessJq` | `string`      | JQ filter to postprocess the json received from the url. |
+| `abi_signature` | `string`      | ABI signature of struct for encoding.                    |
+
+## Response
+
+| Field              | Solidity type | Description       |
+| ------------------ | ------------- | ----------------- |
+| `abi_encoded_data` | `bytes`       | ABI encoded data. |
+
+## Lowest Used Timestamp
+
+For `lowestUsedTimestamp`, `0xffffffffffffffff` ($2^{64}-1$ in hex) is used.
+
+## Verification process
+
+Query the URL with GET method.
+If the query is unsuccessful or does not return a json, reject the request.
+
+Apply the jq filter specified in the request to the received json.
+
+ABI encode the filtered json with the abi_signature provided in the request and return it as abi_encoded_data.
+
+`LowestUsedTimestamp` is unlimited.