feat: Add support for "metadata_options" argument

[jeremyciak]

Description

Adding support for the metadata_options argument of the aws_instance resource

Motivation and Context

#191

Breaking Changes

How Has This Been Tested?

[antonbabenko]

Looks good, but I have just a couple of comments.

This addition is not backward compatible with the existing code because it will trigger an update for users who don't specify var.metadata_options.

Could you please update the code to support it (using dynamic block)?

Could you also change from c5.large to something much smaller, so that it is not very $$$ to run in automation?

[jeremyciak]

@antonbabenko please let me know if the latest commit gets this to where you want it to be.

[jeremyciak]

I like your implementation a lot more... I modeled mine after the root_block_device which could probably more appropriately be implemented the same way you've done here. However making that change now would probably break implementations of this module "out in the wild".

[antonbabenko]

Yes, the original implementation was created in pre-0.12 times and I don't want to break it for existing features.

v2.16.0 has been just released.

[yi2020]

@antonbabenko I played around with the new version (thank you) and noticed something odd:
After creating an instance with the module, if you add or remove the metadata_options, Terraform doesn't see that as a reason to rebuild the instance.

[github-actions]

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