Support requirements.sh to install system dependencies

[deliahu]

Description

Allow the user to provide a top-level requirements.sh file (it could be named something else), in which they can install system dependencies.

Motivation

Some dependencies must be installed via apt or via conda

Things to check

• Would this support running in a conda environment?
• chmod +x if necessary

Things to document

• Users would need to run apt-get update before apt-get install
• Building your own image will lead to faster API startup times

[RobertLucian]

Would this support running in a conda environment?

If conda/pip packages are to be installed in this script, then I think this should run by-default in a conda environment. My 2 cents.

[deliahu]

@RobertLucian I just created #852 to track our research into a conda environment separately from this (which can be use primarily for e.g. apt-get install)