feat: add browser configuration for test environment

[aytekin-smartcar]

This PR introduces the ability to configure the web browser used for running tests via an environment variable BROWSER. The valid options for this variable are 'chrome' and 'firefox', with 'firefox' set as the default browser if no environment variable is explicitly defined.

Changes:

• Added BROWSER environment variable configuration to the README, enabling users to choose between Google Chrome or Mozilla Firefox for test executions.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.65%. Comparing base (f622ce2) to head (66e8a2f).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #171 +/- ## ======================================= Coverage 99.65% 99.65% ======================================= Files 6 6 Lines 290 290 ======================================= Hits 289 289 Misses 1 1 ```

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[smartcar-ci]

:tada: This PR is included in version 9.11.0 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: