[FEATURE] Read credentials from environment variables

[bhamail]

Allow Jake to read OSSI and/or IQ credentials from environment variables.

For consistency, should follow the same naming as nancy, eg:

export OSSI_USERNAME=auser@anemailaddress.com
export OSSI_TOKEN=A4@k3@p1T0k3n

and for IQ:

export OSSI_USERNAME=auser@anemailaddress.com
export OSSI_TOKEN=A4@k3@p1T0k3n
export IQ_USERNAME=nondefaultuser
export IQ_TOKEN=yourtoken
export IQ_SERVER=http://adifferentserverurl:port

may relate to Issue #37

cc @bhamail / @DarthHater

[ewohnlich]

I like this, particularly for ddt/ossindex since that doesn't appear to accept any parameters for authentication, unlike IQ/Nexus.

I noticed that ossindex already has the capability to configure authentication https://github.com/sonatype-nexus-community/ossindex-python/blob/main/ossindex/ossindex.py#L60 but the jake CLI doesn't seem to use it. Maybe jake could just instantiate with with these OSSI environment variables if they exist?