add BQ example for databricks_connection (#3040)

Author: nkvuong

docs/resources/connection.md

@@ -12,6 +12,8 @@ This resource manages connections in Unity Catalog
 
 ## Example Usage
 
+Create a connection to a MySQL database
+
 ```hcl
 resource "databricks_connection" "mysql" {
   name            = "mysql_connection"
@@ -29,13 +31,41 @@ resource "databricks_connection" "mysql" {
 }
 ```
 
+Create a connection to a BigQuery database
+
+```hcl
+resource "databricks_connection" "bigquery" {
+  name            = "bq_connection"
+  connection_type = "BIGQUERY"
+  comment         = "this is a connection to BQ"
+  options = {
+    GoogleServiceAccountKeyJson = jsonencode({
+      "type" : "service_account",
+      "project_id" : "PROJECT_ID",
+      "private_key_id" : "KEY_ID",
+      "private_key" : "-----BEGIN PRIVATE KEY-----\nPRIVATE_KEY\n-----END PRIVATE KEY-----\n",
+      "client_email" : "SERVICE_ACCOUNT_EMAIL",
+      "client_id" : "CLIENT_ID",
+      "auth_uri" : "https://accounts.google.com/o/oauth2/auth",
+      "token_uri" : "https://accounts.google.com/o/oauth2/token",
+      "auth_provider_x509_cert_url" : "https://www.googleapis.com/oauth2/v1/certs",
+      "client_x509_cert_url" : "https://www.googleapis.com/robot/v1/metadata/x509/SERVICE_ACCOUNT_EMAIL",
+      "universe_domain" : "googleapis.com"
+    })
+  }
+  properties = {
+    purpose = "testing"
+  }
+}
+```
+
 ## Argument Reference
 
 The following arguments are supported:
 
 - `name` - Name of the Connection.
 - `connection_type` - Connection type. `BIGQUERY` `MYSQL` `POSTGRESQL` `SNOWFLAKE` `REDSHIFT` `SQLDW` `SQLSERVER` or `DATABRICKS` are supported. [Up-to-date list of connection type supported](https://docs.databricks.com/query-federation/index.html#supported-data-sources)
-- `options` - The key value of options required by the connection, e.g. `host`, `port`, `user` and `password`.
+- `options` - The key value of options required by the connection, e.g. `host`, `port`, `user`, `password` or `GoogleServiceAccountKeyJson`. Please consult the [documentation](https://docs.databricks.com/query-federation/index.html#supported-data-sources) for the required option.
 - `owner` - (Optional) Name of the connection owner.
 - `properties` -  (Optional) Free-form connection properties.
 - `comment` - (Optional) Free-form text.
@@ -44,7 +74,7 @@ The following arguments are supported:
 
 In addition to all arguments above, the following attributes are exported:
 
-* `id` - ID of this connection in form of `<metastore_id>|<name>`.
+- `id` - ID of this connection in form of `<metastore_id>|<name>`.
 
 ## Import