Added color field in environment model and ui

[shashank-lol]

PR Description

This pull request implements the color selection feature for an environment from a predefined set of 8 colors. This color will be visible in the Environment pane at the top right .

Implementation Details

1. Downgraded the freezed dependency to 2.5.7 in all the packages as I wasn't able to change the Environment model to add a color field. Since all the packages had a v3.0.6 freezed dependency but the main project had it to the lower version.
2. Added a Color parameter in the Env model and created a small dot widget along with the name in the dropdown menu and environments pane.
3. Updated the test for validation of environments json by adding a color parameter there also.

Screenshots

Related Issues

• Closes Adding color support for environments #601

Checklist

• I have gone through the contributing guide
• I have updated my branch and synced it with project main branch before making this PR
• I am using the latest Flutter stable branch (run flutter upgrade and verify)
• I have run the tests (flutter test) and all tests are passing

Added/updated tests?

We encourage you to add relevant test cases.

• Yes
• No, and this is why: please replace this line with details on why tests have not been included

OS on which you have developed and tested the feature?

• Windows
• macOS
• Linux

[ashitaprasad]

@shashank-lol You can refer to the the feedback here - #601 (comment)