Only select chunks from submissions that match the given key-value set

> As the AI team we are also interested in a new strategy: `SelectOnly`
>
> From https://github.com/channable/opsqueue/blob/master/doc/proposals/strategies_and_metadata.md:
>
> ```
> /// Only select chunks from submissions that match the given key-value set when submission
> SelectOnly(meta_field: String, value: MetaValue, underlying: Strategy)
> ```
>
> For us it would be a key ingredient in implementing blue/green deployments for our AI model. The `meta_field` would then be the model version.

_Originally posted by @SemMulder in [#95](https://github.com/channable/opsqueue/issues/95#issuecomment-4978958634)_