chore(java): use "software.amazon.awscdk.core" for core module

[eladb]

use software.amazon.awscdk.core as the java package name for the core package, so it won't conflict with the old "cdk" package which used software.amazon.awscdk.core

misc: include sdk-api-metadata.json in @aws-cdk/custom-resources

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[mergify]

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