Move internal packages to an internal folder

For reference: https://go.dev/doc/go1.4#internalpackages

internal/integration/pinboard/pinboard.go

@@ -0,0 +1,52 @@
+// SPDX-FileCopyrightText: Copyright The Miniflux Authors. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package pinboard // import "miniflux.app/v2/internal/integration/pinboard"
+
+import (
+	"fmt"
+	"net/url"
+
+	"miniflux.app/v2/internal/http/client"
+)
+
+// Client represents a Pinboard client.
+type Client struct {
+	authToken string
+}
+
+// NewClient returns a new Pinboard client.
+func NewClient(authToken string) *Client {
+	return &Client{authToken: authToken}
+}
+
+// AddBookmark sends a link to Pinboard.
+func (c *Client) AddBookmark(link, title, tags string, markAsUnread bool) error {
+	if c.authToken == "" {
+		return fmt.Errorf("pinboard: missing credentials")
+	}
+
+	toRead := "no"
+	if markAsUnread {
+		toRead = "yes"
+	}
+
+	values := url.Values{}
+	values.Add("auth_token", c.authToken)
+	values.Add("url", link)
+	values.Add("description", title)
+	values.Add("tags", tags)
+	values.Add("toread", toRead)
+
+	clt := client.New("https://api.pinboard.in/v1/posts/add?" + values.Encode())
+	response, err := clt.Get()
+	if err != nil {
+		return fmt.Errorf("pinboard: unable to send bookmark: %v", err)
+	}
+
+	if response.HasServerFailure() {
+		return fmt.Errorf("pinboard: unable to send bookmark, status=%d", response.StatusCode)
+	}
+
+	return nil
+}