springboot Clarify the type to which connection-pool-specific spring.datasource properties are bound

For issue: #20688, Minor change to description of Hikari Datasource properties in documentation

Fixes gh-20688

Comment From: wilkinsona

Thanks very much for making your first contribution to Spring Boot, @parameswaranvv. In reviewing the changes, I realised that they were applicable to Commons DBCP2 and Tomcat JDBC as well. I made similar updates for both of those in a polishing commit. I also had to drop the use of backticks around the class name as the column in the table was rendering them as-is. Apologies for the bad suggestion there.