Fix awsmigrationhub build error

[LilyWangLL]

Issue #, if available:

Description of changes: Change project AWSMigrationHub name from aws-cpp-sdk-AWSMigrationHub to aws-cpp-sdk-awsmigrationhub, fix build error:

CMake Error at cmake/dependencies.cmake:16 (get_target_property):
  get_target_property() called with non-existent target
  "aws-cpp-sdk-awsmigrationhub".
Call Stack (most recent call first):
  cmake/dependencies.cmake:73 (compute_links)
  cmake/sdks.cmake:288 (sort_links)
  CMakeLists.txt:328 (add_sdks)

CMake Error at cmake/dependencies.cmake:84 (get_target_property):
  get_target_property() called with non-existent target
  "aws-cpp-sdk-awsmigrationhub".
Call Stack (most recent call first):
  cmake/sdks.cmake:288 (sort_links)
  CMakeLists.txt:328 (add_sdks)

I'm not sure if the directory name of the project aws-cpp-sdk-AWSMigrationHub also needs to be changed to lowercase. Can you help confirm? cc @sdavtaker

Check all that applies:

• [ ] Did a review by yourself.
• [ ] Added proper tests to cover this PR. (If tests are not applicable, explain.)
• [ ] Checked if this PR is a breaking (APIs have been changed) change.
• [ ] Checked if this PR will not introduce cross-platform inconsistent behavior.
• [ ] Checked if this PR would require a ReadMe/Wiki update.

Check which platforms you have built SDK on to verify the correctness of this PR.

• [ ] Linux
• [x] Windows
• [ ] Android
• [x] MacOS
• [ ] IOS
• [ ] Other Platforms

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[dg0yt]

~I think the bug is in the vcpkg port.~ This sub-project is really inconsistent with regard to its siblings.

[sbiscigl]

So with regard to how things are named and why inconsistencies exist, everything in the directory generated is generated by our model codegen. When i say "model" that is every single aws service provides us with a model file and we use those to auto generate the directory names and class names.

aws migration hub specifically can be found here

and in there we can see "targetPrefix":"AWSMigrationHub", which is why this is named the way it is. So if it were to change anywhere it would change here.

We however do not own this configuration and it is owned by the migration hub service and is provided to us. We try not to make one-off code generation changes because we then have to support a specific service by service customization going forward. We also cant change the name of this currently because people may already rely on it and changing it would create a backward incompatible change.

With the concern of backwards compatibility breakage, and the fact the model comes from upstream i'm against changing this to support a branching model of how we handle the name of the directory. That said I do understand why the inconsistency is not fun.

closing the PR but if you want to talk more about how code gen effects the names of things feel free to re-open and reply.

[dg0yt]

I think the bug is in the vcpkg port.

Now I can confirm that this is a vcpkg bug.