Allow set managed_resource_email via charm config

[Jose Phillips]

Allow set via charm the configuration on designate.conf

# Email to use for managed resources like domains created by the FloatingIP API
#managed_resource_email = <email address hidden>.

all the soa records for floating IP is creating with <email address hidden>

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/charm-designate/+/807029

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/charm-designate/+/807029
Committed: https://opendev.org/openstack/charm-designate/commit/0ac8aefbb8883d314245d1535f0953015678e2fa
Submitter: "Zuul (22348)"
Branch: master

commit 0ac8aefbb8883d314245d1535f0953015678e2fa
Author: Jose Phillips <email address hidden>
Date: Thu Sep 2 01:24:49 2021 -0500

    Allow Set managed_resource_email on designate config.

    With this patch managed_resource_email can be set via charm
    with juju config managed-resource-email = <email address hidden>
    functional for auto generated SOA records. that came from
    Floating IP.

    Closes-Bug: #1940864
    Change-Id: I9f55564316fdb559481909dd7b196ef8fd9fe612