Django email builder - add system to assign templates to email & gather queries to create tokens

### Circumstances

Updating our Django transactional emails right now currently involves an inordinate amount of engineering time and deploy resources. We're abstracting it away so we can bring on product and marketing to help manage emails.

### Description

Email epic: https://www.notion.so/gitcoin/Gitcoin-Email-Accountability-06ed4107dd654488b562fb7b9d08e386

After the WYSWYG builder is implemented, we have to set up a system for updating transactional emails using pre-built templates that allow for dynamic data.

For example, if we want to show a list of bounties, a specific bounty, or a list of hackathons, the engineers have to build those tokens in so the product or marketing team can literally drag and drop data they need from our DB to build emails.

Here is the current list of transactional emails: https://www.notion.so/gitcoin/Gitcoin-Email-Accountability-06ed4107dd654488b562fb7b9d08e386#7f0388363f5c40f082d7364566ea67e6