refactor(parameters): BaseProvider support for Uint8Array

[dreamorosi]

Description of your changes

This PR introduces some changes to the typing in BaseProvider so that it's now able to handle, transform, or return Uint8Array objects without necessarily coercing them to string.

The change came from the fact that AWS Secrets Manager can return both string (when the secret is stored as SecretString) and pure binaries aka Uint8Array (when the secret is stored as SecretBinary).

Consumers of the library should be able to both retrieve the latter and have them automatically transformed by the Parameters utility but also have them returned as-is (Uint8Array) in case they don't want to apply any transform.

The PR enables the behavior described above.

The PR introduces also some light housekeeping around dependencies (switches from @aws-sdk/util-base64-node to @aws-sdk/util-base64 due to the former having being marked as being on a deprecation path) and the introduction of the DEFAULT_PROVIDERS object which is required by the other providers.

How to verify this change

See status checks under this PR.

Related issues, RFCs

Issue number: #1172

PR status

Is this ready for review?: YES
Is it a breaking change?: NO

Checklist

• My changes meet the tenets criteria
• I have performed a self-review of my own code
• I have commented my code where necessary, particularly in areas that should be flagged with a TODO, or hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding changes to the examples
• My changes generate no new warnings
• The code coverage hasn't decreased
• I have added tests that prove my change is effective and works
• New and existing unit tests pass locally and in Github Actions
• Any dependent changes have been merged and published
• The PR title follows the conventional commit semantics

Breaking change checklist

• I have documented the migration process
• I have added, implemented necessary warnings (if it can live side by side)

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[dreamorosi]

Given that at this time only DynamoDBProvider, SSMProvider, and SecretsProvider return types are fairly clear, we'll leave the linked issue open after merging this PR, as there might be some additional refactoring needed.