chore: refactor declarative config functionality

Remove the config service and wrap its functionality into the Kong
client.

CHANGELOG.md

@@ -50,9 +50,14 @@
 
 > Release date: 2023/02/03
 
-- **Breaking change** to `ConfigService.ReloadDeclarativeRawConfig()`. Its
-  response signature is now `([]byte, error)`. The byte slice is the config
-  response body. The error is unchanged.
+- **Breaking change:** the `ConfigService` is now directly embedded in the
+  `kong.Client`. Configurations are collections of entities, not entities
+  themselves, so they do not fit with other go-kong services.
+- **Breaking change:** `ReloadDeclarativeRawConfig()` (formerly part of
+  `ConfigService`, now part of `kong.Client`) now has the response signature
+  `([]byte, error)` instead of `error`. The byte slice is the config response
+  body. The error is unchanged.
+  [#273](https://github.com/Kong/go-kong/pull/273)
 
 ## [v0.36.0]
 

kong/client.go

@@ -39,7 +39,6 @@ type Client struct {
 	workspace               string       // Do not access directly. Use Workspace()/SetWorkspace().
 	workspaceLock           sync.RWMutex // Synchronizes access to workspace.
 	common                  service
-	Configs                 AbstractConfigService
 	ConsumerGroupConsumers  AbstractConsumerGroupConsumerService
 	ConsumerGroups          AbstractConsumerGroupService
 	Consumers               AbstractConsumerService
@@ -378,3 +377,45 @@ func (c *Client) RootJSON(ctx context.Context) ([]byte, error) {
 func (c *Client) BaseRootURL() string {
 	return c.baseRootURL
 }
+
+// ReloadDeclarativeRawConfig sends out the specified config to configured Admin
+// API endpoint using the provided reader which should contain the JSON
+// serialized body that adheres to the configuration format specified at:
+// https://docs.konghq.com/gateway/latest/production/deployment-topologies/db-less-and-declarative-config/#declarative-configuration-format
+// It returns the response body and an error, if it encounters any.
+func (c *Client) ReloadDeclarativeRawConfig(
+	ctx context.Context,
+	config io.Reader,
+	checkHash bool,
+) ([]byte, error) {
+	type sendConfigParams struct {
+		CheckHash int `url:"check_hash"`
+	}
+	var checkHashI int
+	if checkHash {
+		checkHashI = 1
+	}
+	req, err := c.NewRequest("POST", "/config", sendConfigParams{CheckHash: checkHashI}, config)
+	if err != nil {
+		return []byte{}, fmt.Errorf("creating new HTTP request for /config: %w", err)
+	}
+
+	resp, err := c.DoRAW(ctx, req)
+	if err != nil {
+		return []byte{}, fmt.Errorf("failed posting new config to /config: %w", err)
+	}
+	defer resp.Body.Close()
+
+	var b []byte
+	if resp.StatusCode < 200 || resp.StatusCode >= 400 {
+		b, err = io.ReadAll(resp.Body)
+		if err != nil {
+			return nil,
+				fmt.Errorf(`failed posting new config to /config: got status code %d
+				(and failed to read the response body): %w`,
+					resp.StatusCode, err)
+		}
+	}
+
+	return b, nil
+}