Persist job inputs spec in Ci::Build options field

What does this MR do and why?

This MR updates Seed::Build so that when a job has inputs defined, we:

1. Store the input definitions in the options field
2. Create Ci::JobInput records with default values <- To keep the ci_job_inputs table small, we've decided to only store values when they differ from the default

It also updates existing job inputs code to expect the input type definition to be stored under a field named type (not input_type as previously defined)

Issue: Persist job inputs spec in Ci::Build options field (#557879)

References

Spike MR: Draft: Spike: Implement CI job inputs keyword (!202106 - closed)

How to set up and validate locally

This MR isn't meant to be validated locally. The next MR will add the inputs keyword to Entry::Job, at which point we'll be able to demonstrate the entire job inputs flow locally