Use HTTP.jl's retry layer instead of Retry in http_request

[iamed2]

The check there seems pretty similar to the RetryLayer in HTTP.jl, but the RetryLayer handles more of HTTP.jl's failure cases. This would require JuliaWeb/HTTP.jl#259 in order to handle the AWSCore-specific failure cases (e.g., ParseError).

[samoconnor]

This seems sensible in principle.
Do you have a use case where it is causing a practical problem?

I don't think the ParseError case is actually ever used. I can' think of a real recoverable situation where HTTP would return a ParseError.
There is other detail to consider, like here where streaming responses are handled. Where as in HTTP.jl here they are simply treated as non-retryable.
Also AWSCore.jl retries requests which HTTP.jl would consider to be non-idempotent. We'd have to think about the impact of that a bit.