Allow adding MySQL init_commands to override TX Isolation, Wait Timeout, etc.

[janusman]

Is your feature request related to a problem? Please describe.
Allow adding MySQL init_commands to override TX Isolation, Wait Timeout, etc.

Describe the solution you'd like
Could there be an environment variable that, when set before inclusion of the drupal-recommended-settings file, could have the needed additions?

For example:

setenv("ACQUIA_DB_INIT_TX_ISOLATION", "READ-COMMITTED");
setenv("ACQUIA_DB_WAIT_TIMEOUT", "3600");
// include the drs settings file here

Describe alternatives you've considered
If not this, perhaps at least document an alternate method to do this, similar to https://docs.acquia.com/acquia-cloud-platform/mysql-transactions#section-resolving-deadlocks-by-overriding-the-mysql-transaction-isolation-level-setting

Additional context
Add any other context or screenshots about the feature request here.

[jpmcneal]

+1 Something like this would really help people using DRS.