Implementation: Add maxHeaderSize Decrypt input

[lavaleri]

proposal: https://github.com/awslabs/aws-encryption-sdk-specification/blob/master/proposals/2020-06-26_decrypt-max-header-size-max-body-size/proposal.md

Add input to Decrypt that bounds the allowable size of headers that can be decrypted.

• Java Add maxHeaderSize Decrypt option aws/aws-encryption-sdk-java#205
• Python Add max_header_size Decrypt input aws/aws-encryption-sdk-python#283
• JS Add maxHeaderSize Decrypt Input aws/aws-encryption-sdk-javascript#388
• C Add maxHeaderSize Decrypt option aws/aws-encryption-sdk-c#560
• CLI Expose MaxHeaderSize on Decrypt aws/aws-encryption-sdk-cli#175