Implement parser for pipfile.lock

What does this MR do?

Introduce dependency file parser for Pipfile.lock.

The parser is NOT enabled/imported in main.go because this is currently blocked by gitlab-org/gitlab#33341 (closed).

Also, this parser is redundant with Pipfile parser, enabled in gemnasium-python (see pipenv.go).

What are the relevant issue numbers?

gitlab-org/gitlab#33227 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer
• Remove main.go line 31 after MR is accepted
• Revert changes in .gitlab-ci.yml after MR is accepted. Changes are just for testing purposes