Update artifact coordinates for R2DBC Postgres driver

[mp911de]

With the migration from the R2DBC org to the Postgres org, r2dbc-postgres changed its groupId from io.r2dbc to org.postgresql.

[tisonkun]

Hi @mp911de! In spring-gradle-plugins/dependency-management-plugin#319 I notice that when generate a new spring boot application from the starter it still produces:

    runtimeOnly 'io.r2dbc:r2dbc-postgresql'

as the dependency and thus failed since GAV has changed. Do you know whether this issue should be resolved? (Modify the starter generating logic, I think.)

[mp911de]

That's something to be addressed by https://github.com/spring-io/start.spring.io

[wilkinsona]

@tisonkun I have opened spring-io/start.spring.io#881.