feat: [torrust#596] rename common E2E env vars

We should not use specific names (sufix _E2E) for env vars that are not
specidif for E2E tests. These env vars are generic enva vars also used
in production. They only have different values for the E2E test env.

```
TORRUST_INDEX_E2E_CONFIG             -> TORRUST_INDEX_CONFIG
TORRUST_INDEX_E2E_TRACKER_API_TOKEN  -> TORRUST_INDEX_TRACKER_API_TOKEN
TORRUST_INDEX_E2E_AUTH_SECRET_KEY    -> TORRUST_INDEX_AUTH_SECRET_KEY
TORRUST_INDEX_E2E_PATH_CONFIG        -> TORRUST_INDEX_PATH_CONFIG
```

contrib/dev-tools/container/e2e/mysql/run-e2e-tests.sh

@@ -40,7 +40,7 @@ docker ps
 
 # Run E2E tests with shared app instance
 TORRUST_INDEX_E2E_SHARED=true \
-    TORRUST_INDEX_E2E_PATH_CONFIG="./share/default/config/index.e2e.container.mysql.toml" \
+    TORRUST_INDEX_PATH_CONFIG="./share/default/config/index.e2e.container.mysql.toml" \
     TORRUST_INDEX_E2E_DB_CONNECT_URL="mysql://root:root_secret_password@localhost:3306/torrust_index_e2e_testing" \
     cargo test ||
     {

contrib/dev-tools/container/e2e/sqlite/run-e2e-tests.sh

@@ -38,7 +38,7 @@ docker ps
 
 # Run E2E tests with shared app instance
 TORRUST_INDEX_E2E_SHARED=true \
-    TORRUST_INDEX_E2E_PATH_CONFIG="./share/default/config/index.e2e.container.sqlite3.toml" \
+    TORRUST_INDEX_PATH_CONFIG="./share/default/config/index.e2e.container.sqlite3.toml" \
     TORRUST_INDEX_E2E_DB_CONNECT_URL="sqlite://./storage/index/lib/database/e2e_testing_sqlite3.db?mode=rwc" \
     cargo test ||
     {

tests/e2e/config.rs

@@ -9,16 +9,16 @@ use torrust_index::config::{Configuration, Info};
 
 /// The whole `index.toml` file content. It has priority over the config file.
 /// Even if the file is not on the default path.
-const ENV_VAR_CONFIG: &str = "TORRUST_INDEX_E2E_CONFIG";
+const ENV_VAR_CONFIG: &str = "TORRUST_INDEX_CONFIG";
 
 /// Token needed to communicate with the Torrust Tracker
-const ENV_VAR_API_ADMIN_TOKEN: &str = "TORRUST_INDEX_E2E_TRACKER_API_TOKEN";
+const ENV_VAR_API_ADMIN_TOKEN: &str = "TORRUST_INDEX_TRACKER_API_TOKEN";
 
 /// Secret key used to encrypt and decrypt
-const ENV_VAR_AUTH_SECRET_KEY: &str = "TORRUST_INDEX_E2E_AUTH_SECRET_KEY";
+const ENV_VAR_AUTH_SECRET_KEY: &str = "TORRUST_INDEX_AUTH_SECRET_KEY";
 
 /// The `index.toml` file location.
-pub const ENV_VAR_PATH_CONFIG: &str = "TORRUST_INDEX_E2E_PATH_CONFIG";
+pub const ENV_VAR_PATH_CONFIG: &str = "TORRUST_INDEX_PATH_CONFIG";
 
 // Default values
 pub const DEFAULT_PATH_CONFIG: &str = "./share/default/config/index.development.sqlite3.toml";
@@ -34,7 +34,7 @@ pub const ENV_VAR_DB_CONNECT_URL: &str = "TORRUST_INDEX_E2E_DB_CONNECT_URL";
 /// There are two methods to inject the configuration:
 ///
 /// 1. By using a config file: `index.toml`.
-/// 2. Environment variable: `TORRUST_INDEX_E2E_CONFIG`. The variable contains the same contents as the `index.toml` file.
+/// 2. Environment variable: `TORRUST_INDEX_CONFIG`. The variable contains the same contents as the `index.toml` file.
 ///
 /// Environment variable has priority over the config file.
 ///