Add a new bash prologue section in ToolConfigs, for pre-configuring container commands.

[prioux]

A tool config's attributes generally control and adjust the configuration for running a particular tool's control script on a particular cluster.

In the case of a singularity-deployed tool, the environment variable table and the bash prologue and epilogues are all executed within the container.

We need a way to add some configuration code that is run outside of the singularity invokation, and before it.

I suggest a new textarea input in the container section where, just like for the standard bash prologue, an admin can enter bash commands that will be inserted before singularity is invoked.

Purpose: this will allow the admin to configure, say, a SINGULARITY_ENCRYPTION_PASSPHRASE environment variable for encrypted containers.