feat[next]: as_program embedded

[DropD]

Description

This PR is built on top of #1479 and additionally contains a workflow step to generate a function definition for a Program instance, which doesn't have one (because it came from FieldOperator.as_program).

This is of limited usefulness but would enable my_field_op.as_program(...).with_backend(backend=None)(...).

Requirements

• All fixes and/or new features come with corresponding tests.
• Important design decisions have been documented in the approriate ADR inside the docs/development/ADRs/ folder.

If this PR contains code authored by new contributors please make sure:

• All the authors are covered by a valid contributor assignment agreement provided to ETH Zurich and signed by the employer if needed.
• The PR contains an updated version of the AUTHORS.md file adding the names of all the new contributors.