fix: update instructions (step 2) for configuring Flutter platform

[rikvisser-dev]

What does this PR do?

This pull request updates the Flutter project setup instructions and configuration handling in the createFlutter.svelte file. The changes improve the developer experience by simplifying the configuration process and aligning it with common practices.

Updates to configuration handling:

• Modified the configuration setup to use environment variables (.env file) instead of hardcoded constants in the Flutter project. This includes replacing static const String declarations with APPWRITE_PROJECT_ID and APPWRITE_PUBLIC_ENDPOINT environment variables. (src/routes/(console)/project-[region]-[project]/overview/platforms/createFlutter.svelteL40-R42)

Updates to setup instructions:

• Updated the setup instructions to guide developers to copy the .env.example file, rename it to .env, and update the configuration settings, replacing the previous instruction to edit lib/constants/appwrite.dart. (src/routes/(console)/project-[region]-[project]/overview/platforms/createFlutter.svelteL279-R281)

Test Plan

I’ve visually confirmed the content and run all the checks as required by the Contributing Guidelines.

Related PRs and Issues

#2062

Have you read the Contributing Guidelines on issues?

Yes, I have read the guidelines.

[rikvisser-dev]

I had forgotten to change the formatting of the config example. Now it’s ready for review.