Upgrade matrix-mailer (4.93-r0 -> 4.93-r1)

This is a bit misleading, because the old Docker image
was tagged as `4.93.1`. There hasn't been a `4.93.1` version yet though.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/792

roles/matrix-mailer/defaults/main.yml

@@ -7,7 +7,7 @@ matrix_mailer_container_image_self_build_repository_url: "https://github.com/dev
 matrix_mailer_container_image_self_build_src_files_path: "{{ matrix_mailer_base_path }}/docker-src"
 matrix_mailer_container_image_self_build_version: "{{ matrix_mailer_docker_image.split(':')[1] }}"
 
-matrix_mailer_docker_image: "{{ matrix_mailer_docker_image_name_prefix }}devture/exim-relay:4.93.1-r0"
+matrix_mailer_docker_image: "{{ matrix_mailer_docker_image_name_prefix }}devture/exim-relay:4.93-r1"
 matrix_mailer_docker_image_name_prefix: "{{ 'localhost/' if matrix_mailer_container_image_self_build else 'docker.io/' }}"
 matrix_mailer_docker_image_force_pull: "{{ matrix_mailer_docker_image.endswith(':latest') }}"
 
@@ -19,6 +19,8 @@ matrix_mailer_container_user_gid: 101
 # A list of extra arguments to pass to the container
 matrix_mailer_container_extra_arguments: []
 
+matrix_mailer_hostname: "{{ matrix_server_fqn_matrix }}"
+
 matrix_mailer_sender_address: "matrix@{{ matrix_domain }}"
 matrix_mailer_relay_use: false
 matrix_mailer_relay_host_name: "mail.example.com"

roles/matrix-mailer/templates/env-mailer.j2

@@ -6,3 +6,4 @@ SMARTHOST={{ matrix_mailer_relay_host_name }}::{{ matrix_mailer_relay_host_port
 SMTP_USERNAME={{ matrix_mailer_relay_auth_username }}
 SMTP_PASSWORD={{ matrix_mailer_relay_auth_password }}
 {% endif %}
+HOSTNAME={{ matrix_mailer_hostname }}

roles/matrix-mailer/templates/systemd/matrix-mailer.service.j2

@@ -10,6 +10,8 @@ Type=simple
 ExecStartPre=-{{ matrix_host_command_docker }} kill matrix-mailer
 ExecStartPre=-{{ matrix_host_command_docker }} rm matrix-mailer
 
+# --hostname gives us a friendlier hostname than the default.
+# The real hostname is passed via a `HOSTNAME` environment variable though.
 ExecStart={{ matrix_host_command_docker }} run --rm --name matrix-mailer \
 			--log-driver=none \
 			--user={{ matrix_mailer_container_user_uid }}:{{ matrix_mailer_container_user_gid }} \