add an 'installed' tag to extensions

        if url is None:

            continue

        existing = installed_extension_urls.get(normalize_git_url(url), None)

        extension_tags = extension_tags + ["installed"] if existing else extension_tags

        if len([x for x in extension_tags if x in tags_to_hide]) > 0:

            hidden += 1

            continue

        existing = installed_extension_urls.get(normalize_git_url(url), None)

        install_code = f"""<input onclick="install_extension_from_index(this, '{html.escape(url)}')" type="button" value="{"Install" if not existing else "Installed"}" {"disabled=disabled" if existing else ""} class="gr-button gr-button-lg gr-button-secondary">"""

        tags_text = ", ".join([f"<span class='extension-tag' title='{tags.get(x, '')}'>{x}</span>" for x in extension_tags])

                <td>{html.escape(description)}</td>

                <td>{install_code}</td>

            </tr>

        """

        for tag in [x for x in extension_tags if x not in tags]:

            tags[tag] = tag

    code += """

        </tbody>

    </table>

                    install_extension_button = gr.Button(elem_id="install_extension_button", visible=False)

                with gr.Row():

                    hide_tags = gr.CheckboxGroup(value=["ads", "localization"], label="Hide extensions with tags", choices=["script", "ads", "localization"])

                    hide_tags = gr.CheckboxGroup(value=["ads", "localization", "installed"], label="Hide extensions with tags", choices=["script", "ads", "localization", "installed"])

                install_result = gr.HTML()

                available_extensions_table = gr.HTML()