feat(gatsby): add support for microsecond and alternative iso datetime formats

[himynameistimli]

I've pulled this PR against this branch per @freiksenet's request

Original Description

When attempting to use formatString to format dates in GraphQL, we get "Invalid date", which I believe is due to the precision format of seconds.

From what I've seen in other issues/PRs, it seems to be related to the list of formats in type-date.js file. It seems to only have ISO formats with millisecond precision (YYYY-MM-DDTHHmmss.SSS). We're using a python backend api for page generation and their default precision is in microseconds (YYYY-MM-DDTHHmmss.SSSSSS).

I've gone and added additional support for YYYY-MM-DDTHHmmss.SSSSSS and YYYY-MM-DDTHHmmss.SSSSSSZ as well as support for YYYY-MM-DD HHmmss.SSSSSS and YYYY-MM-DD HHmmss.SSSSSSZ

Notes

Per @sidharthachatterjee I tried to add some tests. Please forgive, I'm not so familiar with tests in JS, so I tried to follow from elsewhere to put together the tests. If anyone has any advice or suggestions on how I can improve them, please let me know.

One issue that I've found is after adding the support for microsecond, not only do microseconds validate, but nanoseconds (YYYY-MM-DDTHHmmss.SSSSSSSSS) and any precision validates (e.g. 2018-08-31T23:25:16.0123456789999+02:00) as well. I'm not sure how to interpret it, but I've just skipped tests that pass when in theory should fail. I've also commented out explicit nanosecond precision support until the tests can pass.

Related Issues

Previous PR #12511
Previous related issue #4813
Should also address #11520 @miktirr plz comment

[wardpeet]

@himynameistimli thanks so much for recreating this PR on our graphql refactoring branch! We'll have a look shortly.

[freiksenet]

I've rebased in against master and made this target it, because we merged schema refactoring. I'll merge as soon as this passes CI.

Thanks a lot!

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