feat: add initial support for fleet provisioning

[stuart-warren]

fixes #171

[codecov]

Codecov Report

Attention: Patch coverage is 74.20814% with 57 lines in your changes missing coverage. Please review.

Project coverage is 66.19%. Comparing base (f386de7) to head (204faa8).

Files	Patch %	Lines
fleetprovisioning/fleetprovisioning.go	73.97%	41 Missing and 16 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #540      +/-   ##
==========================================
+ Coverage   65.28%   66.19%   +0.90%     
==========================================
  Files          33       35       +2     
  Lines        1959     2180     +221     
==========================================
+ Hits         1279     1443     +164     
- Misses        584      625      +41     
- Partials       96      112      +16     

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[at-wat]

Thank you for your contribution!
As I haven't used fleet provisioning feature yet, I'm gonna briefly learn the feature before reviewing

[stuart-warren]

I think I'd like to add some options similar to how you have done so in https://github.com/seqsense/aws-iot-device-sdk-go/blob/master/jobs/option.go