Make DB connection pool size configurable

[NikithShetty]

Currently DB connection pool size is hardcoded to 10 here:

shared-kernel/lib/mobility-core/src/Kernel/Storage/Esqueleto/Config.hs

Line 52 in 1cbba86

pool <- liftIO . runLoggerIO checkedLogEnv $ createPostgresqlPoolModified (modifyConn modifyConnString) connStr 10

This value should be taken from config (part of esqDBCfg dhall config) at startup.