[e.cash] Get blog posts

Summary:
Adding the functions and tests that will be used to fetch the blog posts from the new strapi cms
Strapi has a response limit for how many entries it can return at once. It can be upped to 100 which
would cover our existing 81 posts, but obviously that wont work for long so idea here is

get the amount of pages there are from the metadata in the response
loop through that amount and fetch each page of posts
combine the responses in one array that will be returned to getStaticProps in a later diff

Test Plan:
review the functions and tests
npm run test

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D14105