Convert from 'httr' package to 'httr2' package

[gilbertocamara]

According to Hadley:

"httr2 (pronounced hitter2) is a ground-up rewrite of httr that provides a pipeable API with an explicit request object that solves more problems felt by packages that wrap APIs (e.g. built-in rate-limiting, retries, OAuth, secure secrets, and more)."

Associated sits API function
api_cube, api_gdalcubes, api_downloadand api_source_mpc.