Keymaker master key with KMS

[Zhaars]

Implemented basic support of KMS in the keymaker for AMK generation. Introduce the new flag kms_key_policy which describes possible policies for KMS keys. For now only create is supported.

Made a small refactoring of KMS package by creating a new extended common interface for all KMS operations (Keystore - not an ideal name, can think about a better name). Also, create a separate abstraction called KmsClient that should care about all internal stuff for corresponded KMS.

Checklist

• [ ] Change is covered by automated tests
• [ ] The coding guidelines are followed
• [ ] Public API has proper documentation in the Acra documentation site or has PR on documentation repository with new changes
• [ ] CHANGELOG.md is updated (in case of notable or breaking changes)
• [ ] CHANGELOG_DEV.md is updated
• [ ] Benchmark results are attached (if applicable)
• are up-to-date (in case of API changes)