feat: allow passing environment variables in chat UI

[elliotzh]

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 zhangxingzhi/respect-environment-variables-in-chat-ui

  4 files    4 suites   4m 8s ⏱️
243 tests 204 ✅  39 💤 0 ❌
972 runs  816 ✅ 156 💤 0 ❌

Results for commit deb3898.

[github-actions]

SDK CLI Global Config Test Result zhangxingzhi/respect-environment-variables-in-chat-ui

6 tests   6 ✅  1m 13s ⏱️
1 suites  0 💤
1 files    0 ❌

Results for commit deb3898.

[github-actions]

Executor Unit Test Result zhangxingzhi/respect-environment-variables-in-chat-ui

796 tests   796 ✅  3m 45s ⏱️
  1 suites    0 💤
  1 files      0 ❌

Results for commit deb3898.

[github-actions]

Executor E2E Test Result zhangxingzhi/respect-environment-variables-in-chat-ui

246 tests   240 ✅  4m 59s ⏱️
  1 suites    6 💤
  1 files      0 ❌

Results for commit deb3898.

[github-actions]

SDK CLI Test Result zhangxingzhi/respect-environment-variables-in-chat-ui

    4 files      4 suites   1h 5m 5s ⏱️
  783 tests   740 ✅  43 💤 0 ❌
3 132 runs  2 960 ✅ 172 💤 0 ❌

Results for commit deb3898.