feat: add optional .env support for environment configuration

[maishivamhoo123]

Summary

This PR adds optional support for loading environment variables from a .env file to improve local development experience.

Changes

• Load .env file at startup if it exists (ignored if missing)
• Add .env.example with empty default values
• Add .env to .gitignore

Backward Compatibility

• No behavior change if .env is not present
• Existing OS environment variables continue to work
• Production and container-based deployments are unaffected

Related Issue

Closes #1450

[LinkinStars]

@maishivamhoo123 You submitted language and configuration files that should not have been submitted.

[maishivamhoo123]

Sorry sir for the confusion. I won’t repeat this again.
Just to confirm, I should add only the following files:

main.go

.env.example

.gitignore

README.md

go.mod
@LinkinStars Sir Please let me know if this is correct.
Thank you for your guidance, sir.

[LinkinStars]

Sorry sir for the confusion. I won’t repeat this again. Just to confirm, I should add only the following files:

main.go

.env.example

.gitignore

README.md

go.mod @LinkinStars Sir Please let me know if this is correct. Thank you for your guidance, sir.

@maishivamhoo123 I think we can skip modifying README.md. We can add this instructions to https://answer.apache.org/docs/env

[maishivamhoo123]

Understood, @LinkinStars sir.
So instead of modifying README.md, I should add the relevant instructions to the documentation at https://answer.apache.org/docs/env
.
Thank you for your guidance.

[maishivamhoo123]

@LinkinStars Sir,
I hope this PR looks good now. If there are any remaining issues or further improvements needed, please let me know—I’ll be happy to address them.

Thank you for your guidance .

[LinkinStars]

@maishivamhoo123 I verified this feature, and it has issues. It fails to correctly read environment variables via .env. This is clearly because the current environment variables are not read within the function itself, but rather within the var scope.

answer/internal/install/install_main.go

Line 31 in 3000e3a

port = os.Getenv("INSTALL_PORT")

Therefore, using godotenv.Load in init() does not ensure all environment variables are properly assigned.

[maishivamhoo123]

Thank you @LinkinStars Sir for your review. You are right, package-level variables are defined before init() runs.

I have fixed this by defining the variables globally and assigning their values inside the init() function. I ran the test and it is running fine: