fix: update node-fetch to 3.x

[RishikeshDarandale]

node-fetch is now ESM module only, thus this will be a breaking change and will requires at least Node.js 12.20.0.

As suggested by node-fetch, async import() function is used to load node-fetch asynchronously.

BREAKING CHANGE: requires at least node 12.20.0

Related: #143 #154

[RishikeshDarandale]

@developit , test cases are failing for me and I am stuck in one of the test case where node-fetch needs to be mocked-up.

[paul-phan]

Hope you take a look @developit