BE: Chore: standarize Protobuf import paths

[yeikel]

What changes did you make? (Give an overview)

Before this change, the SchemaRegistryServiceTests tests were failing in Windows with the following exception:

	at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:782)
	... 55 more
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [io.kafbat.ui.service.DeserializationService]: Constructor threw exception
	at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:221)
	at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:117)
	at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:315)
	... 69 more
Caused by: java.lang.NullPointerException: ProtoFile not found for import 'language/language.proto'
	at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:1011)
	at io.kafbat.ui.serdes.builtin.ProtobufFileSerde$ProtoSchemaLoader$1.load(ProtobufFileSerde.java:403)
	at com.squareup.wire.schema.Linker.getFileLinker$wire_schema(Linker.kt:95)

With this change, we are standardizing the import statements to remove backlashes in Windows which fixes the tests :

How Has This Been Tested? (put an "x" (case-sensitive!) next to an item)

• Manually (please, describe, if necessary)
• Unit checks
• Covered by existing automation

Checklist (put an "x" (case-sensitive!) next to all the items, otherwise the build will fail)

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings (e.g. Sonar is happy)
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged

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