bug: [Ionic CLI] Poor Performance when using --configuration flag with ionic serve

# Bug Report

**Ionic version:**

[x] **5.x**

**Current behavior:**

When app is served via `ionic serve --project myProject --configuration=sandbox` the refresh that takes place after changes are saved, is significantly longer than using `ionic serve --project myProject` (Note: no --configuration flag).

**Expected behavior:**

The refresh should take the same amount of time as `ionic serve --project myProject`.

My workaround is to take the contents of **_environment.sandbox.ts_** and copy them into **_environment.ts_**. Then I run `ionic serve --project myProject`. This resolves the slow performance I am seeing.

**Steps to reproduce:**

1. Create a new environment file. (i.e. environment.sandbox.ts)
2. Copy contents of environment.ts into your new environment file.
3. Add the appropriate entries in angular.json.
4. In Ionic CLI, run `ionic serve --project myProject --configuration=yourConfig`

**Ionic info:**

```
Ionic:

Ionic CLI : 6.16.3
Ionic Framework : @ionic/angular 5.6.4
@angular-devkit/build-angular : 0.1102.13
@angular-devkit/schematics : 11.2.13
@angular/cli : 11.2.13
@ionic/angular-toolkit : 3.1.1

Utility:

cordova-res : not installed globally
native-run : not installed globally

System:

NodeJS : v14.17.0 (/usr/local/bin/node)
npm : 6.14.13
OS : macOS Catalina

```