Remember Test Sources root choice and suggest as default #1010

Description

Test sources root chosen by the user in test generation should be remembered and suggested as default the next time.
Currently if the new test sources root utbot-tests is generated - other test root is shown as default in Gradle project.

To Reproduce

1. Run a Maven project in IntelliJ Idea 2022.1.4 - with the newest UTBot plugin build from main installed
2. Test sources root is present in project
3. Open UnitTestBot test generation dialog for a Java class
4. Select utbot-tests to be created as the new test sources root, generate tests
5. Open UnitTestBot dialog once again

Expected behavior

Created test sources root utbot-tests should be selected by default.

Actual behavior

User pre-defined test sources root is selected by default.

Visual proofs (screenshots, logs, images)

Environment

Windows 10 Pro
IntelliJ IDEA 2022.1.4
JDK 8
Maven project