Add support for Rego registration policies (regorus 0.5.0)

[achamayou]

Add support for a "policyRego" field in configuration, similar to "policyScript" but allowing the definition of Rego policies.

A sample policy may be:

package policy

default allow := false

valid_issuer if {
  input.phdr.cwt.iss == "valid_issuer"
}

allow if {
  valid_issuer
}

errors contains "Invalid issuer" if { not valid_issuer }

See documentation for more detail.

All JS policy testcases have been templatised to run a rego equivalent, including performance regression test_perf, which feeds into the bencher dashboard. Performance tests show that equivalent Rego policies cause no performance regression compared to JS.

This replaces #260.