Change DimensionSetExceededException to a checked exception

[markkuhn]

Issue #, if available: #120

Description of changes:
Change DimensionSetExceededException to a checked exception.

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[gordonpn]

Are there tests to make sure that the checked exception are thrown when we expect them to be thrown?

[markkuhn]

Are there tests to make sure that the checked exception are thrown when we expect them to be thrown?

Those tests can be found in DimensionSetTest.java. They were written as part of #103. Since I'm only changing the exception type I didn't need to write new tests.

[jqmichael]

@markkuhn @gordonpn

Returning checked exception made consumer hard to upgrade. I don't think it's a pattern to use checked exception in AWS SDK.

Why unchecked exceptions?
The AWS SDK for Java uses runtime (or unchecked) exceptions instead of checked exceptions for these reasons:

To allow developers fine-grained control over the errors they want to handle without forcing them to handle exceptional cases they aren’t concerned about (and making their code overly verbose)

To prevent scalability issues inherent with checked exceptions in large applications

In general, checked exceptions work well on small scales, but can become troublesome as applications grow and become more complex.

https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/handling-exceptions.html