feat(c/v3-engine): prefix $ for "values" instead of the suffix FromEnv for "keys"

[jjangga0214]

Component

c/v3-engine

Is your proposal related to a problem?

The suffix ~FromEnv is used as a convention for environment variables.

For instance, in the example below, value should be refactored to valueFromEnv to use an env var.

kind: AuthConfig
definition:
  mode:
    jwt:
      key:
        fixed:
          key:
+           valueFromEnv: AUTH_SECRET_AS_ENV_VAR
-           value: "raw-value"

But sometimes, there's no ~FromEnv field.
For example, the snippet below does not work, as there is no field like jwkFromEnv.

kind: AuthConfig
definition:
  mode:
    jwt:
      key:
+       jwkFromEnv: JWK_URL_AS_ENV_VAR
-       jwk: "https://hard-coded-url.com"

In such cases, users should report and request a new feature, like #10592.
This is a bottleneck between core developers and consumers.

Describe the solution you'd like

What if we introduce a prefix like $ for values, instead of the suffix FromEnv for keys?
For example, the field jwk is still used, but the value is changed to $JWK_URL_AS_ENV_VAR.
This indicates it should be interpreted as an env var.

kind: AuthConfig
definition:
  mode:
    jwt:
      key:
+       jwk: $JWK_URL_AS_ENV_VAR
-       jwk: "https://hard-coded-url.com"

Of course, jwk is just an example. We can apply the new convention everywhere.