Merge pull request #14840 from ukleinek/backend-docs

Update Backend docs

diff --cc docs/backends/bind.rst
Simple merge

diff --cc docs/backends/geoip.rst
Simple merge

diff --cc docs/backends/ldap.rst
Simple merge

diff --cc docs/backends/lua2.rst
Simple merge

diff --cc docs/backends/remote.rst
Simple merge

diff --cc docs/backends/tinydns.rst
Simple merge