mysql-router remove-relation does not clear charm settings and does not overwrite after add-relation.

[Pedro Victor Lourenço Fragola]

[Issue description]

Due to LP#2004088 the mysqlrouter.conf file had invalid settings, so the workaround was to remove the mysql-router relation with the unit and add it again.
The folder => /var/lib/mysql/<app-name>-mysql-router/ is not removed and old configuration files remain in the directory with this, when adding the unit again, the charm cannot overwrite the configuration:

configparser.DuplicateSectionError: While reading from '/var/lib/mysql/placement-mysql-router/mysqlrouter.conf' [line 66]: section 'metadata_cache:[\\w$' already exists

full log => https://pastebin.canonical.com/p/27SbxfcqM8/

Old files need to be overwritten or removed.

[Felipe Reyes (freyes)]

the mysql-router charm would need to implement the 'stop' hook, during that stage stop the mysql-router service and remove configuration files generated by the bootstrap process of mysql-router program.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/jammy
Review: https://review.opendev.org/c/openstack/charm-mysql-router/+/902535

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/21.10
Review: https://review.opendev.org/c/openstack/charm-mysql-router/+/902591

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Nicolas Bock <email address hidden>" on branch: stable/21.10
Review: https://review.opendev.org/c/openstack/charm-mysql-router/+/902591

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/focal
Review: https://review.opendev.org/c/openstack/charm-mysql-router/+/902592

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Nicolas Bock <email address hidden>" on branch: stable/focal
Review: https://review.opendev.org/c/openstack/charm-mysql-router/+/902592

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/focal
Review: https://review.opendev.org/c/openstack/charm-mysql-router/+/902593

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Alex Kavanagh <email address hidden>" on branch: stable/focal
Review: https://review.opendev.org/c/openstack/charm-mysql-router/+/902593
Reason: stable/focal is end-of-life and doesn't get published anywhere; really must clean out these old branches. Sorry for the confusion.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/charm-mysql-router/+/902535
Committed: https://opendev.org/openstack/charm-mysql-router/commit/08a33d6759c4012c7ec470fdd2dcd7852b036394
Submitter: "Zuul (22348)"
Branch: stable/jammy

commit 08a33d6759c4012c7ec470fdd2dcd7852b036394
Author: Nicolas Bock <email address hidden>
Date: Tue Aug 1 07:46:53 2023 -0600

    Add cleanup of configuration files on `stop`

    When this subordinate is removed from a unit it leaves its configuration
    files behind. This can become an issue if the subordinate is added back
    to the unit as pointed out in #2004088.

    This change adds a cleanup step to the `stop` hook so that those
    configuration files are removed on the removal of the subordinate charm.

    Closes-Bug: #2004088
    Closes-Bug: #2004089
    Change-Id: Icfca352f29e089aeccd1434d33a573ca1682339a
    Signed-off-by: Nicolas Bock <email address hidden>
    (cherry picked from commit 17595788edd80580624b03a664dd5cdb05bba47f)