File /src/environments/environment.ts does not exist on ng add with Angular 15

`/src/environments/environment.ts` is optional now with Angular 15. Angularfire's schematics should detect this to avoid an error.

### Version info

**Angular:** 15.0.1

**Firebase:** 9.14.0

**AngularFire:** 7.5.0

**Other (e.g. Ionic/Cordova, Node, browser, operating system):** Node 19.1.0, no browser, Ubuntu 22.10

### How to reproduce these conditions

**Failing test unit, Stackblitz demonstrating the problem**

Just run `ng new test123 && cd test123 && ng add @angular/fire`.

**Steps to set up and reproduce**

```
home@daniel-desktop3:/run/user/1000$ ng new test123
Node.js version v19.1.0 detected.
Odd numbered Node.js versions will not enter LTS status and should not be used for production. For more information, please see https://nodejs.org/en/about/releases/.
? Would you like to add Angular routing? No
? Which stylesheet format would you like to use? CSS
CREATE test123/README.md (1061 bytes)
CREATE test123/.editorconfig (274 bytes)
CREATE test123/.gitignore (548 bytes)
CREATE test123/angular.json (2705 bytes)
CREATE test123/package.json (1038 bytes)
CREATE test123/tsconfig.json (901 bytes)
CREATE test123/tsconfig.app.json (263 bytes)
CREATE test123/tsconfig.spec.json (273 bytes)
CREATE test123/.vscode/extensions.json (130 bytes)
CREATE test123/.vscode/launch.json (474 bytes)
CREATE test123/.vscode/tasks.json (938 bytes)
CREATE test123/src/favicon.ico (948 bytes)
CREATE test123/src/index.html (293 bytes)
CREATE test123/src/main.ts (214 bytes)
CREATE test123/src/styles.css (80 bytes)
CREATE test123/src/assets/.gitkeep (0 bytes)
CREATE test123/src/app/app.module.ts (314 bytes)
CREATE test123/src/app/app.component.css (0 bytes)
CREATE test123/src/app/app.component.html (23083 bytes)
CREATE test123/src/app/app.component.spec.ts (959 bytes)
CREATE test123/src/app/app.component.ts (211 bytes)
✔ Packages installed successfully.
Successfully initialized git.
home@daniel-desktop3:/run/user/1000$ cd test123
home@daniel-desktop3:/run/user/1000/test123$ ng add @angular/fire
Node.js version v19.1.0 detected.
Odd numbered Node.js versions will not enter LTS status and should not be used for production. For more information, please see https://nodejs.org/en/about/releases/.
? Would you like to share pseudonymous usage data about this project with the Angular Team
at Google under Google's Privacy Policy at https://policies.google.com/privacy. For more
details and how to change this setting, see https://angular.io/analytics. No
Global setting: enabled
Local setting: disabled
Effective status: disabled
ℹ Using package manager: npm
✔ Found compatible package version: @angular/fire@7.5.0.
✔ Package information loaded.

The package @angular/fire@7.5.0 will be installed and executed.
Would you like to proceed? Yes
✔ Packages successfully installed.
UPDATE package.json (1068 bytes)
✔ Packages installed successfully.
? What features would you like to setup? Authentication, Firestore
Using firebase-tools version 11.16.1
? Which Firebase account would you like to use? test@example.com
✔ Preparing the list of your Firebase projects
? Please select a project: project12345
✔ Preparing the list of your Firebase WEB apps
? Please select an app: project-lab12345
✔ Downloading configuration data of your Firebase WEB app
File /src/environments/environment.ts does not exist
```

**Sample data and security rules**

The Firebase project online is a new and empty project.

### Debug output

** Errors in the JavaScript console **

This is not a runtime problem.

** Output from `firebase.database().enableLogging(true);` **

This is not a runtime problem.

** Screenshots **

Console output pasted above.

### Expected behavior

It should succeed and I should not see any red lines in the terminal.

### Actual behavior

ng add fails at a red line `File /src/environments/environment.ts does not exist` then exits without completing. See the output above.

Now I have to set up angularfire manually. I could have created environment.ts but it would still feel equally manual.