Increase support for the Accept header

[82marbag]

Some smithy clients and servers, such as in Typescript, allow the Accept header to reflect HTTP's spec, by allowing */* and type/*. The smithy spec allows neither of them.

After discussing this change, it was proposed to:

• reflect the HTTP spec regarding the Accept header more closely, allowing *, but no q-factor weighting
• servers should not use Accept to do protocol selection and allow them to respond in any of the allowed (by the header's value) ways

[82marbag]

Related issue in smithy-rs, where we follow more closely the smithy spec: https://github.com/awslabs/smithy-rs/issues/1544

[kstich]

Closed by #1365