jdbc/hikari: rename properties for multi-database usage

[jknack]

Advanced hikari configuration is available via hikari[.dbname.].property. For example:

db.spock.url = "jdbc:mysql://localhost:3306/spock?createDatabaseIfNotExist=true&useSSL=false&serverTimezone=Europe/Rome"
db.spock.user = "root"
db.spock.password = "password"

hikari.spock.maximumPoolSize = 100

db.vulcan.url = "jdbc:mysql://localhost:3306/vulcan?createDatabaseIfNotExist=true&useSSL=false&serverTimezone=Europe/Rome"
db.vulcan.user = "root"
db.vulcan.password = "password"
db.vulcan.cachePrepStmts = true

hikari.vulcan.maximumPoolSize = 50

Here we define two databases: db.spock and db.vulcan. Then we customize poolsize for each of them via hikari.spock.maximumPoolSize and hikari.vulcan.maximumPoolSize

Due to how it works config library, this syntax hikari[.dbname].property breaks/fails at startup time when multiple database are available.

Solution is to prefix hikari properties with database name, like: db.spock.hikari.maximumPoolSize or db.vulcan.hikari.maximumPoolSize