Remove invalid defaults for some services (#3217)

## Motivation and Context
<!--- Why is this change required? What problem does it solve? -->
<!--- If it fixes an open issue, please link to the issue here -->

Some services have generated types with properties that have a default
value of zero. This can cause invalid requests if the service expects a
value > 0.

## Description
<!--- Describe your changes in detail -->

Adds a customization that removes the default value for services with
this issue.

## Testing
<!--- Please describe in detail how you tested your changes -->
<!--- Include details of your testing environment, and the tests you ran
to -->
<!--- see how your change affects other areas of the code, etc. -->
- Added a test for the customization to make sure defaults were removed.
- Generated clients for the impacted services and verified the expected
types had the default value removed.

## Checklist
<!--- If a checkbox below is not applicable, then please DELETE it
rather than leaving it unchecked -->
- [x] I have updated `CHANGELOG.next.toml` if I made changes to the AWS
SDK, generated SDK code, or SDK runtime crates

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Co-authored-by: Russell Cohen <rcoh@amazon.com>