feat(parser): allow to add identifiers

[RomainLanz]

Hey there! 👋🏻

This PR is the continuation of https://github.com/adonisjs/env/pull/35. It adds a way to set up an identifier for an environment variable, helping to interpolate the value of your env.

It can be useful in multiple scenarios.

1. To manage your secrets, you may use a Secrets Vault like Docker Secret or HashiCorp Vault. Doing so it will generate a path for your secret and won't give you any value directly. You can write a custom logic to read the file content.

   DB_PASSWORD=file:/run/secrets/db_password

2. You may encrypt your secrets. You will be able to decrypt them on the fly.

   APP_KEY=encrypted:ksadskjadsjkdasjkdsjdjaskjkdjkasdkj

Env.identifier('file', (value: string) => {
  // ...
})

Env.create(new URL('../', import.meta.url), {
  ....
})

[thetutlage]

A couple of things to keep in mind

• It is going to be a breaking change for this package.
• We will absorb the breaking change in the framework core and hence it can be minor release for @adonisjs/core.
• We should update the README file with the identifier usage
• And also update the docs with the identifier usage.

[RomainLanz]

It is going to be a breaking change for this package.

Why is this a breaking change? The behavior is not changing for current users.

[thetutlage]

We have changed the parse method to async, which was sync earlier.

So anyone relying on this package using the Parser directly (which is publicly exported) has to now await the parse method call

[RomainLanz]

Ah yes, for anyone using the package directly, it is a breaking change, that's true. 😄