Cost Monitoring MVP improvements

[jnywong]

Context

There are a few bugs and improvements to be made before we can consider https://github.com/2i2c-org/jupyterhub-cost-monitoring/ to be a Minimum Viable Product (MVP).

What we need to do

Address the following issues:

• Handle BinderHubs separately jupyterhub-cost-monitoring#31
• Make sure timezones are consistently handled jupyterhub-cost-monitoring#32
• Integration test to validate cost logic jupyterhub-cost-monitoring#34
• [cost-monitoring] Additional terraform flag to separate activation of cost allocation tags #6763

Definition of Done

• Cost logic is validated with software tests