[Batch] Enable async batch if environment is set

[thy09]

Description

Please add an informative description that covers that changes made by the pull request and link all relevant issues.

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 heta/async-batch

  2 files    2 suites   2m 6s ⏱️
243 tests 204 ✅ 39 💤 0 ❌
486 runs  408 ✅ 78 💤 0 ❌

Results for commit 133a619.

[github-actions]

SDK CLI Global Config Test Result heta/async-batch

0 tests   0 ✅  0s ⏱️
0 suites  0 💤
0 files    0 ❌

Results for commit 133a619.

[github-actions]

Executor Unit Test Result heta/async-batch

0 tests   0 ✅  0s ⏱️
0 suites  0 💤
0 files    0 ❌

Results for commit 133a619.

[github-actions]

Executor E2E Test Result heta/async-batch

0 tests   0 ✅  0s ⏱️
0 suites  0 💤
0 files    0 ❌

Results for commit 133a619.

[github-actions]

SDK CLI Test Result heta/async-batch

    2 files      2 suites   31m 57s ⏱️
  783 tests   740 ✅ 43 💤 0 ❌
1 566 runs  1 480 ✅ 86 💤 0 ❌

Results for commit 133a619.

[github-actions]

Hi, thank you for your interest in helping to improve the prompt flow experience and for your contribution. We've noticed that there hasn't been recent engagement on this pull request. If this is still an active work stream, please let us know by pushing some changes or leaving a comment.