Increase hikari.maximum-pool-size

[michaelkain]

This PR increases hikari.maximum-pool-size on ms import (40 to 50) and ms datasets (60 to 70).
This allows to have more db-connections in the pool for parallel user requests in both microservices.
Our MySQL database, version 5.7, that is behind all 6 microservices has a default
max_connections configuration from 151.
With this PR, the max_connections are configured and distributed as follows:

• MS Users: default, 10
• MS Studies: default, 10
• MS Import: now 50
• MS Datasets: now 70
• MS Preclinical: default, 10
• MS NIfTI Conversion: 0, as requires NO connection to database
• SUMMARY: 150 (to relate with the max_numbers supported by MySQL)