Document connection uri parameters for database collectors

[banjoh]

To have the collector's documentation complete, add references of how to construct connection strings of the various databases we support.

• MySQL - https://github.com/go-sql-driver/mysql#parameters
• PostgreSQL - https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-CONNSTRING
• Redis -
• MSSQL - https://learn.microsoft.com/en-us/dotnet/api/system.data.sqlclient.sqlconnection.connectionstring?view=dotnet-plat-ext-7.0