Conform to OPA 0.61.0. (#118)

Implement `import rego.v1`
https://www.openpolicyagent.org/docs/latest/policy-language/#the-regov1-import

- `if` required before rule body
- import rego.v1 automatically imports future.keywords
- handle import shadowing
- data, input cannot be shadowed
- deprecated functions as disallowed
- rules must have assignment or body
- `contains` required for parital set

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

Cargo.toml

@@ -89,7 +89,6 @@ uuid = { version = "1.6.1", features = ["v4", "fast-rng"], optional = true }
 jsonschema = { version = "0.17.1", default-features = false, optional = true }
 chrono = { version = "0.4.31", optional = true }
 chrono-tz = { version = "0.8.5", optional = true }
-document-features = "0.2.8"
 
 
 [dev-dependencies]