RFC: Merge project `approved` and `approval_requested` flags into a single field

# Problem

Looking at these two fields, it really seems they serve a singular purpose.
```Elixir
# A project is created
`approved: false, approval_requested: false`
# User submits project for approval
`approved: false, approval_requested: true`
# Admin approves project
`approved: true, approval_requested :does_not_matter`
```

A single field, for example,

```Elixir
# 'created' -> 'pending_approval' -> 'approved'
field :onboarding_status, :string, null: false, default: 'created'
```

Might serve our purposes much better.

We could add an additional status of `rejected` later, with an additional field of `rejected_reason` or something.