Support parsing query parameters into the ${params} object

[vordimous]

Describe the desired outcome from the user's perspective
As an API admin I need to add more dynamic parameters to a URL query by passing in different query parameters.

Acceptance criteria

• Parse supported URL query parameters into the ${params} object
• Create mechanisms to determine when a parameter is empty or missing
• Handle arrays and allow mapping them to lists in the zilla.yaml

Additional context
/topic?keys=key1,keys=key2,keys=key3 would result in a filter:

      with:
        capability: fetch
        topic: items-snapshots
        filters:
          - key: key1
          - key: key2
          - key: key3

[jfallows]

Perhaps we need to keep the config simple and detect that a specific query parameter is multi-valued.

/topic?keys=key1,keys=key2,keys=key3 would result in a filter:

      with:
        capability: fetch
        topic: items-snapshots
        filters:
          - key: ${params.keys}

... which implicitly expands to the effective filter below:

      with:
        capability: fetch
        topic: items-snapshots
        filters:
          - key: key1
          - key: key2
          - key: key3

Internally I think we'd potentially be able to handle this generally as:

      with:
        capability: fetch
        topic: items-snapshots
        filters:
          - key: key1 OR key2 OR key3

In the case of key this is relatively clear, however when the query parameters map to header filters, then it is less clear if the values should always be ORed or sometimes be ANDed since the same header name can repeat in the same message with different values.