Set correct cgLanguageAssistant in EngineProcess codegen #1918

[volivan239]

Description

After adding cgLanguageAssistant property to CodeGenerator, it was JavaCgLanguageAssistant by default, so anyone who constructs CodeGenerator should set the correct value in constructor. However, this was not done for codegenerator instance in EngineProcessMain, which lead to UtBot action always using Java for codegeneration. This PR sets this parameter correctly in EngineProcessMain and also changes the default value of property to default assistant for passed codegen language.

Fixes #1918

How to test

Manual tests

Just launch UtBot action with "Generated test language" = "Kotlin" on any class, and check that the generated tests is written in Kotlin.

Self-check list

• I've set the proper labels for my PR (at least, for category and component).
• PR title and description are clear and intelligible.
• I've added enough comments to my code, particularly in hard-to-understand areas.
• The functionality I've repaired, changed or added is covered with automated tests.
• Manual tests have been provided optionally.
• The documentation for the functionality I've been working on is up-to-date.