Added CLI beam width functionality

[Sinacam]

What does this PR do?

To document the API of beam_width, models are no longer black boxes and have a public function predict_values.

Test CLI & API (bash tests/autotest.sh)

Test APIs used by main.py.

• [x] Test Pass
  • (Copy and paste the last outputted line here.)
• [ ] Not Applicable (i.e., the PR does not include API changes.)

Check API Document

If any new APIs are added, please check if the description of the APIs is added to API document.

• [x] API document is updated (linear, nn)
• [ ] Not Applicable (i.e., the PR does not include API changes.)

Test quickstart & API (bash tests/docs/test_changed_document.sh)

If any APIs in quickstarts or tutorials are modified, please run this test to check if the current examples can run correctly after the modified APIs are released.