Fixes

Adds support for providing a custom ObjectMapper to the rest client builders. If no ObjectMapper is provided to the builder, a default one which matches the existing configuration will be used. The default ObjectMapper for each rest client type will also now be held in a static variable, so we aren't instantiating a new one every time a rest client is created.

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the Contribution Guidelines and my PR follows them
• I have titled the PR appropriately
• I have updated my branch with the main branch
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation about the functionality in the appropriate .md file
• I have added inline documentation to the code I modified

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