Allow override for createdAt and updatedAt properties

[azrikahar]

Types of changes

• Bug fix (a non-breaking change which fixes an issue)
• New feature (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Description

Resolves: #252

This stems from the linked issue, but I did also thought about this a while ago when considering to retain the datetime if I'm migrating the posts to nuxt/content.

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes (if not applicable, please state why)

I have mentioned that the createdAt and updatedAt properties can be overrided in the docs over here.

I'm not particular sure how we can add tests for this since the original createdAt & updatedAt of the files can be different if I make a new fork of the repo. With that said, I did do some tests myself and here are the test results:

value in content/document	generated value when fetching
2019-02-10	2019-02-10T00:00:00.000Z
20x19-02-10	Falls back to original creation datetime
2019-02-10 10:00	2019-02-10T02:00:00.000Z
2019-02-10 10:00 PM	2019-02-10T14:00:00.000Z
Feb 2019	2019-01-31T16:00:00.000Z
2 2019	Falls back to original creation datetime

Note that my timezone is UTC +8, so there's 8 hours offset for the results with time.

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (dev@be4e58c). Click here to learn what that means.
The diff coverage is n/a.

@@          Coverage Diff           @@
##             dev     #254   +/-   ##
======================================
  Coverage       ?   89.57%           
======================================
  Files          ?       15           
  Lines          ?      547           
  Branches       ?      116           
======================================
  Hits           ?      490           
  Misses         ?       50           
  Partials       ?        7           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update be4e58c...cbc0068. Read the comment docs.

[benjamincanac]

Thanks @azrikahar!