Add new configuration document for connection slack

docs/reference/config-files/connection/slack.md

@@ -0,0 +1,73 @@
+---
+title: slack
+sidebar_label: slack
+---
+
+# slack
+
+The `slack` connection can be used to access Slack resources.
+
+```hcl
+connection "slack" "my_slack" {
+  token = "xoxp-234567890"
+}
+```
+
+## Arguments
+
+| Name    | Type   | Required? | Description             |
+| ------- | ------ | --------- | ----------------------- |
+| `token` | String | Optional  | An API token for slack. |
+
+All arguments are optional, and a `slack` connection with no arguments will behave the same as the [Slack default connection](#default-connection).
+
+## Attributes (Read-Only)
+
+| Attribute | Type | Description                                                                    |
+| --------- | ---- | ------------------------------------------------------------------------------ |
+| `env`     | Map  | A map of the resolved connection-related environment variables (`SLACK_TOKEN`) |
+
+## Default Connection
+
+The Slack connection type includes an implicit, default connection (`connection.slack.default`) that will be configured to set the `token` to the `SLACK_TOKEN` environment variable.
+
+```hcl
+connection "slack" "default" {
+  token = env("SLACK_TOKEN")
+}
+```
+
+## Examples
+
+### Static Connections
+
+```hcl
+connection "slack" "my_slack" {
+  token = "xoxp-234567890"
+}
+```
+
+### Using Slack Connections in HTTP Step
+
+```hcl
+pipeline "gcp_test" {
+  param "connection" {
+    type    = string
+    default = "default"
+  }
+
+  step "http" "list_channels" {
+    url    = "https://slack.com/api/conversations.list"
+    method = "get"
+
+    request_headers = {
+      Content-Type  = "application/json; charset=utf-8"
+      Authorization = "Bearer ${connections.slack[param.connection].token}"
+    }
+
+    request_body = jsonencode({
+      types            = "public_channel"
+    })
+  }
+}
+```