Allow other formats when unmarshalling time

[ItalyPaleAle]

This PR makes the method that unmarshalls times a bit more flexible.

Currently, only dates that are in full RFC339 format are supported, strictly. This adds a couple more formats relaxing the parser:

• 2006-01-02 15:04:05.999999999 -> allows things like 2022-02-10 10:20:30 (nanoseconds are optional)
• 2006-01-02 -> allowing things like 2022-02-10 (which defaults to midnight)

When a time zone is not specified, it defaults to UTC (as the default for time.Parse)

I have:

• Added tests covering the bug / feature (see testing)
• Updated any relevant documentation (see docs)

[giautm]

I think you should mapping Time to your custom scalar instead.

[coveralls]

Coverage increased (+0.04%) to 74.46% when pulling 9a0650b on ItalyPaleAle:unmarshal-time-format into d7da5b0 on 99designs:master.

[ItalyPaleAle]

I think you should mapping Time to your custom scalar instead.

Certainly an option. I still thought of submitting this as it doesn't necessarily change the behavior of the un-marshaller but just adds some more flexibility, for example adding support for formats that work on Postgres and many other places.

Up to the maintainers if they want to consider this or not :)

[giautm]

This PR changes the format to accept date-only layout (2006-01-02) can break other applications that don't expect it.

PS: Time layout format was a very-old issue in the Golang repository. :(