Core implementation for MySQL support

[ptrdom]

Partially resolves #158.
Split off from #170.

[ptrdom]

Unsure how to best deal with configuration differences for different databases, but suggesting alternatives on every setting does not seem very usable for users. Maybe something like https://github.com/lightbend/config?tab=readme-ov-file#inheritance?

[ptrdom]

By inheritance I mean defining groups of settings related to certain databases.

[pjfanning]

Do you have any examples of other configs that have defaults in reference.conf that are not appropriate for mysql users? I'm not against adding mysql specific configs in some cases

[ptrdom]

Config differences between dialects are expressed here:

pekko-persistence-r2dbc/core/src/test/scala/org/apache/pekko/persistence/r2dbc/TestConfig.scala

Lines 24 to 62 in daa27a7

	val dialectConfig = dialect match {
	case "postgres" =>
	ConfigFactory.parseString("""
	pekko.persistence.r2dbc.connection-factory {
	driver = "postgres"
	host = "localhost"
	port = 5432
	user = "postgres"
	password = "postgres"
	database = "postgres"
	}
	""")
	case "yugabyte" =>
	ConfigFactory.parseString("""
	pekko.persistence.r2dbc.connection-factory {
	driver = "postgres"
	host = "localhost"
	port = 5433
	user = "yugabyte"
	password = "yugabyte"
	database = "yugabyte"
	}
	""")
	case "mysql" =>
	ConfigFactory.parseString("""
	pekko.persistence.r2dbc{
	connection-factory {
	driver = "mysql"
	host = "localhost"
	port = 3306
	user = "root"
	password = "root"
	database = "mysql"
	}
	db-timestamp-monotonic-increasing = on
	use-app-timestamp = on
	}
	""")
	}

So different drivers, default ports, credentials, database names, and with MySQL we require following to be set:

db-timestamp-monotonic-increasing = on 
use-app-timestamp = on 

Journal will throw error upon initialization if these settings are in different values.

I will try coming up with something more ergonomic, of course you can provide suggestions if you have preferences.

[pjfanning]

Looking at those, I appreciate the problem but I think in the short term, we could document the set up for the 3 dialects. We could do a follow up PR that makes tries to simplify the set up.

[ptrdom]

All good, I see current documentation already has info for Postgres and Yugabyte - https://pekko.apache.org/docs/pekko-persistence-r2dbc/current/connection-config.html,, so I will add a new tab for MySQL.

[pjfanning]

could you add @since 1.1.0 on new public classes and methods?

[ptrdom]

Ah, forgot to make these new classes private. I think they should be - if users really want to change journal's behavior they can always wire in their own, no need for us to maintain additional public API for that.

[pjfanning]

can you add the same license header from the create sql?

[pjfanning]

can you add a license header like the one on the create sql

[pjfanning]

lgtm - thanks

I'll leave open for a few days to allow others to review

[pjfanning]

I'll merge to unblock projection work