Add contributor "takuya-kihara" and post "AWS Amplify Subscriptions Usage Series"

[tacck]

• Add contributor "takuya-kihara"
• Add post "AWS Amplify Subscriptions Usage Series"

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[watilde]

Kindly asking for review to ship this together: cc @medelman17 @aspittel

[aspittel]

Hey @tacck , sorry for the slow response on this - the project is no longer being maintained but will be replaced with something new soon. Thank you so much for writing about amplify and being a member of the community!