Allow creating rbac with custom id

[codecov[bot]]

Codecov Report

Patch coverage: 86.20% and project coverage change: +0.37 :tada:

Comparison is base (f0b5a1f) 87.19% compared to head (b1e11d2) 87.57%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #33 +/- ## ========================================== + Coverage 87.19% 87.57% +0.37% ========================================== Files 24 24 Lines 1203 1231 +28 Branches 79 81 +2 ========================================== + Hits 1049 1078 +29 - Misses 133 136 +3 + Partials 21 17 -4 ``` | [Impacted Files](https://app.codecov.io/gh/uditha-atukorala/gatekeeper/pull/33?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Uditha+Atukorala) | Coverage Δ | | |---|---|---| | [src/datastore/rbac-policies.h](https://app.codecov.io/gh/uditha-atukorala/gatekeeper/pull/33?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Uditha+Atukorala#diff-c3JjL2RhdGFzdG9yZS9yYmFjLXBvbGljaWVzLmg=) | `77.77% <ø> (ø)` | | | [src/service/grpc.cpp](https://app.codecov.io/gh/uditha-atukorala/gatekeeper/pull/33?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Uditha+Atukorala#diff-c3JjL3NlcnZpY2UvZ3JwYy5jcHA=) | `78.65% <69.23%> (+0.16%)` | :arrow_up: | | [src/datastore/rbac-policies.cpp](https://app.codecov.io/gh/uditha-atukorala/gatekeeper/pull/33?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Uditha+Atukorala#diff-c3JjL2RhdGFzdG9yZS9yYmFjLXBvbGljaWVzLmNwcA==) | `93.61% <100.00%> (+1.17%)` | :arrow_up: | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/uditha-atukorala/gatekeeper/pull/33/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Uditha+Atukorala)

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