[IJ Plugin] Play nice with IDEs without Kotlin/Gradle

[BoD]

Some inspections were running (and trying to load Kotlin specific classes) even when in IDEs without the Kotlin plugin - e.g. RustRover. This could break the whole language support.

In general this PR makes things smoother in IDEs other than IJ/AS:

• Make inspections run only with specific file types
• Move all components specific to Apollo Kotlin to the Kotlin plugin dependency file
• Do not load services that can't work without the Kotlin and Gradle plugins
• Hide settings that are irrelevant without the Kotlin and Gradle plugins
• Mark the Gradle plugin as optional

[svc-apollo-docs]

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Build ID: 46a767eb0fc68fe423462f16