Go binding: Start implementation of the Aggregate module

## Go binding: Finish implementation of the Aggregate module

| Item | Detail |
|---------|-----------------------|
| Binding | `Go` |
| Module | `Morphir.SDK.Aggregate` |
| Relevant Morphir.IR.SDK module| [`Morphir.IR.SDK.Aggregate`](https://github.com/finos/morphir-elm/blob/main/src/Morphir/IR/SDK/Aggregate.elm)
| Relevant `morphir-jvm` code |[`morphir.sdk.Aggregate`](https://github.com/finos/morphir-jvm/blob/main/morphir/sdk/core/src/morphir/sdk/Aggregate.scala) |
| Relevant Elm Module | [`Aggregate`](https://github.com/finos/morphir-elm/blob/main/src/Morphir/SDK/Aggregate.elm)|

Provide a Go lang implementation of the `Morphir.SDK.Aggregate` module for `Morphir.SDK`.

The implementation should include all the functionality for Aggregate as well as tests (we are willing to have this split across PRs).

Please place it here: https://github.com/finos/morphir/tree/features/polyglot-morphir/corelib/go/morphir/sdk/

Start by comparing Morphir.IR.SDK.Aggregate, the Elm Aggregate module, and morphir.sdk.Aggregate in morphir-jvm, then inspect corelib/go/morphir/sdk/. Implement the corresponding Morphir.SDK.Aggregate functionality there and add tests covering all supported operations; done means the Go module and its tests provide equivalent Aggregate behavior.

Written by the indexing model from the issue text.