Add dotenv to allow router to read environment variables from .env file

.changesets/feat_feature_dotenv.md

@@ -0,0 +1,13 @@
+### Add dotenv to allow router to read environment variables from .env file ([PR #6117](https://github.com/apollographql/router/pull/6117))
+
+Router will now read environment variables from `.env` file. This is helpful for local development to inject in `APOLLO_KEY` and `APOLLO_GRAPH_REF` from a `.env` file. It also makes these environment variables available everywhere they are currently available such as in rhai scripts:
+
+```
+# .env
+MY_COOL_VARIABLE="yeaaaaa man!"
+
+# main.rhai
+log_info(`MY_COOL_VARIABLE: ${env::get("MY_COOL_VARIABLE")}`);
+```
+
+By [@andrewmcgivery](https://github.com/andrewmcgivery) in https://github.com/apollographql/router/pull/6117

Cargo.lock

@@ -267,6 +267,7 @@ dependencies = [
  "dhat",
  "diff",
  "displaydoc",
+ "dotenvy",
  "ecdsa",
  "flate2",
  "fred",
@@ -2250,6 +2251,12 @@ dependencies = [
  "syn 2.0.76",
 ]
 
+[[package]]
+name = "dotenvy"
+version = "0.15.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1aaf95b3e5c8f23aa320147307562d361db0ae0d51242340f558153b4eb2439b"
+
 [[package]]
 name = "downcast"
 version = "0.11.0"

apollo-router/Cargo.toml

@@ -272,6 +272,7 @@ bytesize = { version = "1.3.0", features = ["serde"] }
 ahash = "0.8.11"
 itoa = "1.0.9"
 ryu = "1.0.15"
+dotenvy = "0.15.7"
 
 [target.'cfg(macos)'.dependencies]
 uname = "0.1.1"

apollo-router/src/executable.rs

@@ -331,6 +331,8 @@ pub fn main() -> Result<()> {
     #[cfg(feature = "dhat-ad-hoc")]
     create_ad_hoc_profiler();
 
+    dotenvy::dotenv()?;
+
     let mut builder = tokio::runtime::Builder::new_multi_thread();
     builder.enable_all();
     if let Some(nb) = std::env::var("APOLLO_ROUTER_NUM_CORES")