Email configuration cannot be changed at runtime

[nscuro]

Current Behavior

We currently use the quarkus-mailer extension to send emails in the notification-publisher.

The configuration of Mailer cannot be changed dynamically at runtime. Instead, it is initialized once on startup. https://stackoverflow.com/questions/70090456/how-to-change-mail-config-quarkus-at-runtime

hyades/notification-publisher/src/main/resources/application.properties

Lines 69 to 77 in e517e93

	## SMTP Mailer
	#
	quarkus.mailer.from=""
	quarkus.mailer.host=""
	quarkus.mailer.port=
	quarkus.mailer.start-tls=DISABLED
	quarkus.mailer.username="'
	quarkus.mailer.password=""
	quarkus.mailer.ssl=false

As part of #929, we need to support modifications to the email configuration via UI. This means that the configuration must reload while the application is running.

The Quarkus Mailer uses Vert.x MailClient behind the scenes. We might need to construct MailClient instances at runtime. The Vert.x docs show how it can be done:

MailConfig config = new MailConfig();
config.setHostname("mail.example.com");
config.setPort(587);
config.setStarttls(StartTLSOptions.REQUIRED);
config.setUsername("user");
config.setPassword("password");
MailClient mailClient = MailClient.create(vertx, config);

The docs also mention connection pooling:

The client can use a connection pool of the SMTP connections to get rid of the overhead of connecting each time to the server, negotiating TLS and login (this function can be turned off by setting keepAlive = false). A client can either be shared or non-shared, if it is shared, the same connection pool will be used for all clients using the same identifier.

This means it could be too expensive to construct a new client for every notification. We will need to find a way to cache MailClient instances until the underlying configuration changes.

Steps to Reproduce

N/A

Expected Behavior

The email configuration should be configurable via UI.

Hyades Version

0.5.0-SNAPSHOT

Repository Type

Hyades services

Browser

N/A

Checklist

• I have read and understand the contributing guidelines
• I have checked the existing issues for whether this defect was already reported

[nscuro]

Working on this as part of #1229