Added Env. Variable Suggestions for JSON request body

[MohamedKamal000]

PR Description

The suggestion box for env variables now appear on top of the json request editor when it gets triggered

Related Issues

• Closes Env. Variable Support for JSON request body #592

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

[MohamedKamal000]

i have tried to add the highlighting for the variable itself inside the JSON editor, but I couldn't; the JsonField does not allow for external style injection
the current JsonTextFieldEditor is tightly coupled with JsonField Widget which uses its own regExp internally for each style we pass to it and the styles are fixed. I can't add a custom style for a certain regexExpression I want.