Housekeeping: replace admin footer block with an `{% include 'inc/footer.html' %}`

[bryanculver]

Would it be possible/sensible to replace this block with an {% include 'inc/footer.html' %} similar to what was done in nautobot/core/templates/base.html below? I think this footer is identical, but would be good to confirm.

Originally posted by @glennmatthews in https://github.com/nautobot/nautobot/pull/2046#discussion_r920128907