docs: document on updating the application icon on core and wear apps

[renancaraujo]

Extracted from #481

Description
As defined by #481 , people using our templates want to know how to update the application icons.

This card is about researching a step-by-step on how to perform this task, maybe using current tools such as Flutter laucher icons.

Then document the findings.

[Salonikansal2]

assign please

[Salonikansal2]

Here what i have tried to make it EASY to understand for a beginner .hope you like it @renancaraujo @alestiago

1. Set Up the Configuration:
   Automatically generate a configuration file with this command:

flutter pub run flutter_launcher_icons:generate
This creates a flutter_launcher_icons.yaml file in your project's root directory.

If you want to specify a custom configuration file name, use:

flutter pub run flutter_launcher_icons:generate -f

To override an existing config file, use the -o flag:

flutter pub run flutter_launcher_icons:generate -o

Alternatively, you can add your Flutter Launcher Icons configuration to your pubspec.yaml file. Here's an example configuration:

dev_dependencies:
flutter_launcher_icons: "^0.13.1"

flutter_launcher_icons:
android: "launcher_icon"
ios: true
image_path: "assets/icon/icon.png"
min_sdk_android: 21
web:
generate: true
image_path: "path/to/image.png"
background_color: "#hexcode"
theme_color: "#hexcode"
windows:
generate: true
image_path: "path/to/image.png"
icon_size: 48
macos:
generate: true
image_path: "path/to/image.png"

2. Run the Package:

After configuring, run the package with these commands:

flutter pub get
flutter pub run flutter_launcher_icons

If you used a custom configuration file name, specify it like this:

flutter pub get
flutter pub run flutter_launcher_icons -f
Ensure your config file is located in the same directory as pubspec.yaml.

Attributes:

You can customize various attributes in the configuration file, such as the image path and specific settings for Android, iOS, web, Windows, and macOS platforms.
Flavor Support:

If you have flavor support, create a configuration file for your flavor following the same format as the main configuration.

Troubleshooting:

If you encounter issues like color differences or image size problems, follow the troubleshooting guidance provided in the documentation
.
Be aware of potential compatibility issues with dependencies and resolve them accordingly.

[alestiago]

@Salonikansal2 thanks for adding the information, would you mind opening a Pull Request with the change so the team can review it?