Enhance support to allow multiple labels with multiple values.

[srhdb]

Description

Currently, prom-label-proxy only allows filtering by a single label, even if multiple values can be specified. For example:

sh --label namespace --label-values namespace1 --label-values namespace2

However, there is no way to filter queries based on multiple labels simultaneously.

Proposed Solution

Introduce support for specifying multiple labels, each with multiple possible values, using a more compact syntax, such as:

sh --labels namespace|database_id --label-values namespace1,namespace2|1,2

This would allow filtering queries where at least one of the specified label-value conditions is met.

Use Case

This feature would improve flexibility when working with metrics that doesn't share the same fields (e.g., namespace and database_id). With this feature, users would be able to filter by multiple labels simultaneously, each having multiple allowed values, all within a single query.

Would this be feasible to implement? Looking forward to your thoughts!

[simonpasquier]

My first reaction is to worry about the additional complexity in the proxy logic to support multiple labels (I can imagine many edge cases). A workaround would to chain multiple prom-label-proxies, each filtering on a specific label.

[mutefiRe]

I opened #190 some time ago, which I think is closely related - might make sense to consider them together.