Any available action to add content before and after sidebar?

You can create your own actions using do_action, like this:

<?php do_action('before_sidebar'); // you can name it whatever you want ?>
<?php if ( is_active_sidebar('main-sidebar') ) : ?>
    <ul>
        <?php dynamic_sidebar('main-sidebar'); ?>
    </ul>
<?php endif; ?>
<?php do_action('after_sidebar'); ?>

and use add_action() normally:

add_action('before_sidebar', 'before_sidebar_function');
add_action('after_sidebar', 'after_sidebar_function');

UPDATE:
depending on the codex you can use wp_meta hook:

Runs when the sidebar.php template file calls the wp_meta function, to
allow the plugin to insert content into the sidebar.

but it should be added by theme authors.

This page might be helpful Full Action Hooks Reference.