DPLT-1044 Add context.fetchFromSocialApi

[morgsmccauley]

ref: #131

This PR limits the fetch function exposed to the VM to only api.near.social. This limits the potential security vulnerabilities that come with exposing fetch as is.

[gabehamilton]

I think it'd be worth putting the fetchLatestSocialBlock method on the context so we keep it locked down. It's oddly specific code to have in the runner but it keeps things locked down.

[morgsmccauley]

@gabehamilton what is the motive for keeping things locked down? Is there risk in exposing fetch?

[morgsmccauley]

@gabehamilton maybe we can have fetchFromSocialApi which is hardcoded to the social API endpoint? That seems limited enough to prevent any damage, but still flexible enough to support a wide variety of use cases?

[gabehamilton]

fetchFromSocialApi sounds great

[morgsmccauley]

Only adding to imperative as it doesn't make sense in a functional context, in most cases you want to use the result of fetch.