Add option to set default Moment.js locale

[kripod]

It would be convenient if there was a global option (e.g. in gatsby-config.json) to set the default locale used for Moment.js in GraphQL queries. Websites made for a non-English audience are harder to maintain because something like locale: "hu" shall always be added to date queries.

[pieh]

Here's where gatsby sets default locale - https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby/src/schema/infer-graphql-type.js#L150 if anyone want to try adding this feature

[sedubois]

Ideally this should be integrated in an i18n plugin, for websites which need to support multiple locales.

[KyleAMathews]

Due to the high volume of issues, we're closing out older ones without recent activity. Please open a new issue if you need help!