Smithy reference architecture identity base APIs

[SergeyRyabinin]

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Description of changes:

Check all that applies:

• [ ] Did a review by yourself.
• [ ] Added proper tests to cover this PR. (If tests are not applicable, explain.)
• [ ] Checked if this PR is a breaking (APIs have been changed) change.
• [ ] Checked if this PR will not introduce cross-platform inconsistent behavior.
• [ ] Checked if this PR would require a ReadMe/Wiki update.

Check which platforms you have built SDK on to verify the correctness of this PR.

• [ ] Linux
• [ ] Windows
• [ ] Android
• [ ] MacOS
• [ ] IOS
• [ ] Other Platforms

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