Refactor pipeline to extract reusable basepipeline in module and library

[tdruez]

This PR refactors the pipelines architecture to extract a reusable BasePipeline in its own module and also available as standalone library

This is going to support adopting pipelines in VulnerableCode and PurlDB

Reference:

• https://github.com/nexB/scancode.io/issues/1351
• https://github.com/nexB/vulnerablecode/issues/1509
• https://github.com/nexB/purldb/issues/521

[tdruez]

The code in this branch is currently experimental and not ready for merge/production.

[tdruez]

This PR is already too complex combining the module refactoring, the Pipeline classes refactoring, packaging logic, and new CI for release publishing.

Let's split this into manageable and simpler-to-review parts:

• [x] Move the current BasePipeline class to a new aboutcode.pipeline module without any code logic changes. https://github.com/nexB/scancode.io/pull/1357
• [x] Refactor the BasePipeline to remove the scanpipe.Project logic and make it reusable without Project context. https://github.com/nexB/scancode.io/pull/1358
• [x] Add the packaging and release system https://github.com/nexB/scancode.io/pull/1359