Add required property to defineConditionKeys to be used for serviceResolvedConditionKeys

[0xjjoyy]

Background

• What do these changes do?

1. Adds a required property to the IAM trait defineConditionKeys.
2. Updates the IAM trait documentation.

• Why are they important?

Defines whether a service resolved condition key is required. Not applicable to request resolved condition keys as the native @required trait must be used on the field directly.

Testing

• How did you test these changes?

1. Smithy test files.
2. Java test class to check required is set correctly.

Links

• Links to additional context, if necessary
• Issue #, if applicable (see here for a list of keywords to use for linking issues)

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[kstich]

It appears there are also checkstyle validations that are failing the build.

[kstich]

Resolving in favor of #2288