Add Warrant as open-source Zanzibar equivalent

[MaxwellBo]

As per this blog post

After reading the seminal Zanzibar paper, we decided to build Warrant’s core authorization engine based on many of the concepts described in the paper (e.g. tuples, namespaces, zookies, etc. – more on these concepts later). We believed that Zanzibar had zeroed in on a set of fundamental concepts and patterns that would help us build a generic solution to the authorization challenges of any application.

[MaxwellBo]

@jhuangtw bumping

[MaxwellBo]

@jhuangtw bumping again

[MaxwellBo]

@jhuangtw bumping again

[MaxwellBo]

@jhuangtw bumping agian