docs: fix links to OPA docs (aquasecurity#6480)

docs/docs/advanced/air-gap.md

@@ -137,6 +137,6 @@ $ trivy conf --skip-policy-update /path/to/conf
 ```
 
 [allowlist]: ../references/troubleshooting.md
-[oras]: https://oras.land/cli/
+[oras]: https://oras.land/docs/installation
 
 [^1]: This is only required to scan `jar` files. More information about `Java index db` [here](../coverage/language/java.md)

docs/docs/scanner/misconfiguration/custom/index.md

@@ -101,9 +101,8 @@ In this case, `user.*` will be evaluated.
 Any package prefixes such as `main` and `user` are allowed.
 
 ### Metadata
-Metadata helps enrich Trivy's scan results with useful information.
 
-The annotation format is described in the [OPA documentation](https://www.openpolicyagent.org/docs/latest/annotations/).
+The check must contain a [Rego Metadata](https://www.openpolicyagent.org/docs/latest/policy-language/#metadata) section. Trivy uses standard rego metadata to define the new policy and general information about it.
 
 Trivy supports extra fields in the `custom` section as described below.
 

docs/docs/scanner/misconfiguration/custom/schema.md

@@ -88,4 +88,4 @@ To use such a policy with Trivy, use the `--config-policy` flag that points to t
 $ trivy --config-policy=/Users/user/my-custom-policies <path/to/iac>
 ```
 
-For more details on how to define schemas within Rego policies, please see the [OPA guide](https://www.openpolicyagent.org/docs/latest/schemas/#schema-annotations) that describes it in more detail.
+For more details on how to define schemas within Rego policies, please see the [OPA guide](https://www.openpolicyagent.org/docs/latest/policy-language/#schema-annotations) that describes it in more detail.