docs: Add 8 to 9 migration guide (#2039)

Author: mykola-mokhnach

README.md

@@ -6,10 +6,15 @@
 
 This is the Java language bindings for writing Appium Tests that conform to [WebDriver Protocol](https://w3c.github.io/webdriver/)
 
-## v8 Migration
+## v8 to v9 Migration
+
+Since v9 the client only supports Java 11 and above.
+Follow the [v8 to v9 Migration Guide](./docs/v8-to-v9-migration-guide.md) in order to streamline the migration process.
+
+## v7 to v8 Migration
 
 Since version 8 Appium Java Client had several major changes, which might require to 
-update your client code. Make sure to follow the [v7 to v8 Migration Guide](https://github.com/appium/java-client/blob/master/docs/v7-to-v8-migration-guide.md)
+update your client code. Make sure to follow the [v7 to v8 Migration Guide](./docs/v7-to-v8-migration-guide.md)
 in order to streamline the migration process.
 
 ## Add Appium java client to your test framework
@@ -90,6 +95,7 @@ dependencies {
 ### Compatibility Matrix
  Appium Java Client | Selenium client
 --------------------|-----------------
+ `9.0.0`            | `4.14.1`
  `8.5.0`, `8.5.1`   | `4.9.1`, `4.10.0`, `4.11.0`, `4.12.0`, `4.12.1` (known issue: appium/java-client#2004), `4.13.0`
  `8.4.0`            | `4.8.2`, `4.8.3`, `4.9.0`
  `8.3.0`            | `4.7.0`, `4.7.1`, `4.7.2`, `4.8.0`, `4.8.1`

docs/v8-to-v9-migration-guide.md

@@ -0,0 +1,46 @@
+This is the list of main changes between major versions 8 and 9 of Appium 
+java client. This list should help you to successfully migrate your 
+existing automated tests codebase. 
+
+
+## The support for Java compilers below version 11 has been dropped 
+
+- The minimum supported Java version is now 11. The library won't work
+with Java compilers below this version.
+
+## The minimum supported Selenium version is set to 4.14.1
+
+- Selenium versions below 4.14.1 won't work with Appium java client 9+.
+Check the [Compatibility Matrix](../README.md#compatibility-matrix) for more
+details about versions compatibility.
+
+## Removed previously deprecated items
+
+- `MobileBy` class has been removed. Use 
+[AppiumBy](../src/main/java/io/appium/java_client/AppiumBy.java) instead
+- `launchApp`, `resetApp` and `closeApp` methods along with their
+`SupportsLegacyAppManagement` container. 
+Use [the corresponding extension methods](https://github.com/appium/appium/issues/15807) instead.
+- `WindowsBy` class and related location strategies.
+- `ByAll` class has been removed in favour of the same class from Selenium lib.
+- `AndroidMobileCapabilityType` interface. Use 
+[UIAutomator2 driver options](../src/main/java/io/appium/java_client/android/options/UiAutomator2Options.java) 
+or [Espresso driver options](../src/main/java/io/appium/java_client/android/options/EspressoOptions.java) instead.
+- `IOSMobileCapabilityType` interface. Use 
+[XCUITest driver options](../src/main/java/io/appium/java_client/ios/options/XCUITestOptions.java) instead.
+- `MobileCapabilityType` interface. Use 
+[driver options](../src/main/java/io/appium/java_client/remote/options/BaseOptions.java) instead.
+- `MobileOptions` class. Use
+[driver options](../src/main/java/io/appium/java_client/remote/options/BaseOptions.java) instead.
+- `YouiEngineCapabilityType` interface. Use
+[driver options](../src/main/java/io/appium/java_client/remote/options/BaseOptions.java) instead.
+- Several misspelled methods. Use properly spelled alternatives instead.
+- `startActivity` method from AndroidDriver. Use 
+[mobile: startActivity](https://github.com/appium/appium-uiautomator2-driver#mobile-startactivity) 
+extension method instead.
+- `APPIUM` constant from the AutomationName interface. It is not needed anymore.
+- `PRE_LAUNCH` value from the GeneralServerFlag enum. It is not needed anymore.
+
+## Moved items
+
+- `AppiumUserAgentFilter` class to `io.appium.java_client.internal.filters` package.