feat: add user-level parameter autofill (#11731)

This PR solves #10478 by auto-filling previously used template values in create and update workspace flows.

I decided against explicit user values in settings for these reasons:

* Autofill is far easier to implement
* Users benefit from autofill _by default_ — we don't need to teach them new concepts
* If we decide that autofill creates more harm than good, we can remove it without breaking compatibility

docs/api/users.md

@@ -513,6 +513,57 @@ curl -X PUT http://coder-server:8080/api/v2/users/{user}/appearance \
 
 To perform this operation, you must be authenticated. [Learn more](authentication.md).
 
+## Get autofill build parameters for user
+
+### Code samples
+
+```shell
+# Example request using curl
+curl -X GET http://coder-server:8080/api/v2/users/{user}/autofill-parameters?template_id=string \
+  -H 'Accept: application/json' \
+  -H 'Coder-Session-Token: API_KEY'
+```
+
+`GET /users/{user}/autofill-parameters`
+
+### Parameters
+
+| Name          | In    | Type   | Required | Description              |
+| ------------- | ----- | ------ | -------- | ------------------------ |
+| `user`        | path  | string | true     | User ID, username, or me |
+| `template_id` | query | string | true     | Template ID              |
+
+### Example responses
+
+> 200 Response
+
+```json
+[
+  {
+    "name": "string",
+    "value": "string"
+  }
+]
+```
+
+### Responses
+
+| Status | Meaning                                                 | Description | Schema                                                              |
+| ------ | ------------------------------------------------------- | ----------- | ------------------------------------------------------------------- |
+| 200    | [OK](https://tools.ietf.org/html/rfc7231#section-6.3.1) | OK          | array of [codersdk.UserParameter](schemas.md#codersdkuserparameter) |
+
+<h3 id="get-autofill-build-parameters-for-user-responseschema">Response Schema</h3>
+
+Status Code **200**
+
+| Name           | Type   | Required | Restrictions | Description |
+| -------------- | ------ | -------- | ------------ | ----------- |
+| `[array item]` | array  | false    |              |             |
+| `» name`       | string | false    |              |             |
+| `» value`      | string | false    |              |             |
+
+To perform this operation, you must be authenticated. [Learn more](authentication.md).
+
 ## Get user Git SSH key
 
 ### Code samples