feat: set or update environment variables dynamically (#1476)

[SeiwonPark]

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PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

Currently we can get environment variables and set cache. But there's no feature for setting environment variables dynamically. This could be useful even when testing the server locally so to make it dynamically updated when reloaded.

Issue Number: #1476

What is the new behavior?

This PR adds feature for setting/updating environment variables with the method set in ConfigService. And as @nestjs/config depends of dotenv-expand to resolve interpolation, I could get hint from NOT being interpolated.

So after getting environment paths from module's config, simply can parse the environment variables as raw strings (I mean, like the option expandVariables to false). And then simply just replacing interpolated variables too.

This resolves #1476

Does this PR introduce a breaking change?

• Yes
• No

[carlosmesas-acciona]

When will this improvement be brought to production? I find it interesting

[SeiwonPark]

@kamilmysliwiec Could you review this PR? Or is there anything else that I need to do here?

[skypencil]

What is the status on this PR?

[w0aw]

if i create an api endpoint (all it does just change env variable at runtime using this.configService.set() method) will it change output of configService.get() immidiately ? or it will try to override .env file?

because in most cases in prod (when using docker/ k8s) we don't have .env file. ideal solution would be set config variables in memory in place of environment level

[kamilmysliwiec]

LGTM