Add mixin to help convert blobs to string

[kuhe]

Describe the feature

#2252

There is a widely supported request for a convenient way to convert a lambda invocation response (blob) to string.
This can be done with some user code, but we can also apply an official mixin method to make it easier for users.

Use Case

lambda invocation response payload

Proposed Solution

apply a mixin similar to the one used for Streaming collectors in https://github.com/aws/aws-sdk-js-v3/tree/main#streams

Other Information

No response

Acknowledgements

• I may be able to implement this feature request

SDK version used

3.222.0

Environment details (OS name and version, etc.)

all

[RanVaknin]

related: #2123

[kuhe]

work on this will include the issue described in #4786

PR #4836 address payload blobs automatic string conversion

Some blobs are not payloads and should be addressed separately. For non-payload blobs, the solution should involve expanding the toUtf8 and therefore the interface Encoder from smithy types from (Uint8Array => string) to (string | Uint8Array => string). However, that is a breaking change and will require some design consideration.

[kuhe]

• payload blobs (like Lambda::invoke's input and output) now accept strings on input and convert easily to strings on output.
• the potential second half of this feature would be to make non-payload blobs automatically convert from string to Uint8Array. This can be seen for example in The example of SendRawEmailCommand does not match the docs so the example fails if you try to replicate #4800.