fix(env-collector): add .json support and add documentation

libs/env-collector/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "env-collector"
-version = "0.1.0"
+version = "0.1.1"
 edition = "2021"
 
 [dependencies]

libs/env-collector/README.md

@@ -0,0 +1,60 @@
+Env collector
+===
+
+This is a simple tool to collect possible environment variables from `Settings` structure and place it to `README.md` file.
+
+## Usage
+
+1. Add `env-collector` to your `server` crate:
+    ```toml
+    # Cargo.toml
+    [dependencies]
+    env-collector = { git = "https://github.com/blockscout/blockscout-rs", version = "0.1.1" }
+    ```
+
+2. In your `server` crate create new binary file called `check-envs.rs` with the following content:
+
+    ```rust
+    // check-envs.rs
+    use <path_to_settings>::Settings;
+    use env_collector::run_env_collector_cli;
+
+    fn main() {
+        run_env_collector_cli::<Settings>(
+            "<SERVICE_NAME_PREFIX>",
+            "README.md",
+            "<PATH TO .TOML/.JSON EXAMPLE CONFIG>",
+            &["<ENV_PREFIX_TO_IGNORE>"],
+        );
+    }
+    ```
+3. In `README.md` file add special **anchors** lines to specify where to store the table with ENVs:
+
+    ```markdown
+    ## Envs
+
+    [anchor]: <> (anchors.envs.start)
+    [anchor]: <> (anchors.envs.end)
+    ```
+
+4. (Optional) In your `justfile` add new command to run `check-envs.rs`:
+
+    ```just
+    # justfile
+    check-envs:
+        cargo run --bin check-envs
+    ```
+
+5. Run command `just check-envs` to generate ENVs table in `README.md` file.
+
+6. Add github action to run this binary on every push to validate ENVs table in `README.md` file:    
+    ```yaml
+    [... other steps of `test` job ...]
+
+    - name: ENVs in doc tests
+      run: cargo run --bin check-envs
+      env:
+        VALIDATE_ONLY: true
+
+    [... other steps of `test` job ...]
+      ```