support serving engine switch in pf serve cmd

[wxpjimmy]

Description

Add --engine parameter in pf flow serve command, customer can use this parameter to switch the python serving engine between flask and fastapi, it's default to flask

All Promptflow Contribution checklist:

• The pull request does not introduce [breaking changes].
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.
• Create an issue and link to the pull request to get dedicated review from promptflow team. Learn more: suggested workflow.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[github-actions]

promptflow SDK CLI Azure E2E Test Result xiaopwan/support_serving_engine_switch_in_pf_serve_cmd

  4 files    4 suites   4m 9s ⏱️
242 tests 205 ✅  37 💤 0 ❌
968 runs  820 ✅ 148 💤 0 ❌

Results for commit f5e97f4.

♻️ This comment has been updated with latest results.

[github-actions]

SDK CLI Global Config Test Result xiaopwan/support_serving_engine_switch_in_pf_serve_cmd

6 tests   6 ✅  1m 10s ⏱️
1 suites  0 💤
1 files    0 ❌

Results for commit f5e97f4.

♻️ This comment has been updated with latest results.

[github-actions]

Executor Unit Test Result xiaopwan/support_serving_engine_switch_in_pf_serve_cmd

792 tests   792 ✅  3m 45s ⏱️
  1 suites    0 💤
  1 files      0 ❌

Results for commit f5e97f4.

♻️ This comment has been updated with latest results.

[github-actions]

Executor E2E Test Result xiaopwan/support_serving_engine_switch_in_pf_serve_cmd

243 tests   238 ✅  5m 32s ⏱️
  1 suites    5 💤
  1 files      0 ❌

Results for commit f5e97f4.

♻️ This comment has been updated with latest results.

[github-actions]

SDK CLI Test Result xiaopwan/support_serving_engine_switch_in_pf_serve_cmd

    4 files      4 suites   1h 3m 9s ⏱️
  714 tests   673 ✅  41 💤 0 ❌
2 856 runs  2 692 ✅ 164 💤 0 ❌

Results for commit f5e97f4.

♻️ This comment has been updated with latest results.