I have created a gravity form and would like to programmatically submit it. I want to create a template in WordPress that is a custom HTML form, all the data then get's submitted to the actual form for the Gravity Forms logic to occur.
Check out the GFAPI::submit_form() method:
https://docs.gravityforms.com/api-functions/#submit-form
You can take the data submitted in the HTML form, format the data into a structure that Gravity Forms expects and then pass it to this function to trigger an artificial submission.