This is the exact plugin you need - https://wordpress.org/plugins/gallery-custom-links/

No code customizations needed. 

For fixed image link (http://www.example.com):

 

    $args = array(
    'post_type' => 'post',
    'name' => 'partners'
    );
    $logo_img = new WP_Query( $args );
    ?>
    <div class="container-fluid" id="">
      <div class="row" style="margin-top:1em;margin-bottom:1em;">
    <?php if( $logo_img->have_posts() ): while( $logo_img->have_posts() ): $logo_img->the_post();
    $logo_gallery = get_post_gallery_images( $post->ID );
    if( $logo_gallery ): ?>
      <div class="col-sm-12 col-md-12 col-lg-12 text-center">
    <?php foreach($logo_gallery as $logo ): ?>
    	<a href="http://www.example.com">
        <img class="img-fluid" src="<?php echo $logo; ?>" alt="" width="60" id="partner-logo" style="margin:0 .5em 0 .5em;"/>
    	</a>
    <?php endforeach; ?>
      </div>
    <?php endif; ?>
    <?php endwhile; ?>
    <?php endif; wp_reset_postdata(); ?>
      </div>
    </div>