New Event Tracking Features

[jrtashjian]

This PR adds enhanced event tracking features to OmniForm. Here's what's new:

• Impression Tracking: Logs every time a form is viewed.
• Submission Tracking: Records both successful and failed form submissions.
• Conversion Rate: Calculates the conversion rate based on unique impressions and successful submissions.

To implement event tracking efficiently, two new tables have been added:

• Events Table: Stores details of form interactions like impressions and submissions.
• Visitors Table: Maintains unique visitor hashes to identify users without storing personal data (inspired by Plausible).

These tables are designed to handle millions of records, ensuring quick query performance and optimized storage. The flexible schema allows for tracking additional events in the future, helping users continually improve the effectiveness of their forms.

Closes #29