Changed the Flutter version, Kotlin version, and few dependency libraries

[tamojitalwaysghosh]

Fixes #211

Changes that have been made -

pubspec.yaml:

1. changed flutter version: sdk: ">=2.7.0 <3.0.0" to sdk: ">=3.2.3 <4.0.0"
2. updated few dependencies

App-level build.gradle:

1. upgraded - compileSdkVersion 31 --> 32 - buildToolsVersion '29.0.0' --> '33.0.0' - targetSdkVersion 30 --> 32
2. Replaced 'com.android.support:multidex:1.0.3' with 'androidx.multidex:multidex:2.0.1'

android/build.gradle:

1. Removed deprecated jcenter(): Replaced with mavenCentral().
2. Upgraded plugin versions: android-gradle-plugin:7.1.0 --> 7.4.0
3. Set kotlin_version: ext.kotlin_version = '1.6.10' --> ‘1.7.10’

Note: Please check Allow edits from maintainers. if you would like us to assist in the PR.