Please allow to override default_soa_expire by charm

[Nobuto Murata]

Designate upstream has some default values for SOA record, and allows to override the default by designate.conf. Also, it looks like Designate does not allow those SOA values to be overwritten per zone with API requests:
https://bugs.launchpad.net/designate/+bug/1784271

As it cannot be modified with APIs, it would be nice if designate charm allows to override those default in designate.conf as charm options.

====
# SOA refresh-min value (integer value)
# Deprecated group/name - [DEFAULT]/default_soa_refresh
#default_soa_refresh_min = 3500

# SOA max value (integer value)
#default_soa_refresh_max = 3600

# SOA retry (integer value)
#default_soa_retry = 600

# SOA expire (integer value)
#default_soa_expire = 86400

# SOA minimum value (integer value)
#default_soa_minimum = 3600
====

Exposing all options may be too much. So default_soa_expire would be sufficient since it has a shorter default value (86400s = 1d) compared to RFC 1912 suggestion (2-4 weeks).

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/586939

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/586939
Committed: https://git.openstack.org/cgit/openstack/charm-designate/commit/?id=068d30461a237da0c7fafacaaeee4352694b13df
Submitter: Zuul
Branch: master

commit 068d30461a237da0c7fafacaaeee4352694b13df
Author: Nobuto Murata <email address hidden>
Date: Mon Jul 30 14:31:16 2018 +0900

    Allow overriding the default default_soa_expire

    Designate upstream has a shorter default value of SOA expire as
    86400s=1d than RFC 1912 suggestion (2-4 weeks). So allow tweaking the
    default value per operational needs.

    Change-Id: I668a4470be612e596ab4db73ece0c37269c88005
    Closes-Bug: #1784272