Timeouts refactor (#1246)

* rename: in aws_smithy_types, timeout::TimeoutConfig is now timeout::Config
update: timeout::Config now wraps 3 config structs (Http, Tcp, Api)
update: aws_config timeout setting to work with timeout::Config changes
update: providers to work with new timeout config structure
update: codegen to work with new timeout config structure
update: CHANGELOG.next.toml

* add: missing copyright header

* update: impl From instead of Into for timeout conf
fix: clippy lints

* fix: service config codegen for timeouts

* fix: broken doc tests

* fix: bad doc link

* update: transfer aws_types::Config changes to new aws_types::SdkConfig

* fix: two outdated doc tests

* Apply suggestions from code review

Co-authored-by: John DiSanti <jdisanti@amazon.com>

* undo: doc change for timeout env vars
refactor: move parse_str_as_timeout to aws_config and privatize it
update: aws_config code for parse_str_as_timeout
move
remove: comments from private struct members
update: comments for pub struct methods

Co-authored-by: John DiSanti <jdisanti@amazon.com>