Fix return value when host property does not exist from data.selector

[eguzki]

What

Selectors in rules[].data.selector[] have a default named attribute to cover the use case where the property does not exist https://github.com/Kuadrant/wasm-shim/blob/main/src/configuration.rs#L7-L20

pub struct SelectorItem {
    // Selector of an attribute from the contextual properties provided by kuadrant
    // during request and connection processing
    pub selector: String,

    // If not set it defaults to `selector` field value as the descriptor key.
    #[serde(default)]
    pub key: Option<String>,

    // An optional value to use if the selector is not found in the context.
    // If not set and the selector is not found in the context, then no data is generated.
    #[serde(default)]
    pub default: Option<String>,
}

When the selector property does not exist, the behavior is ruled by the default field. Currently the implementation was enforcing a default value (empty string "") defeating the purpose of the default attribute.

Verification Steps

• Run development env

  make development

The wasm configuration applied for *.a.com is

{
                              "name": "rlp-ns-A/rlp-name-A",
                              "domain": "rlp-ns-A/rlp-name-A",
                              "service": "limitador",
                              "hostnames": ["*.a.com"],
                              "rules": [
                                {
                                  "data": [
                                    {
                                      "selector": {
                                        "selector": "unknown.path"
                                      }
                                    }
                                  ]
                                }
                              ]
                            }

• Run request

  curl -H "Host: test.a.com" http://127.0.0.1:18000/get

  Data selector should not generate return any value. Thus, descriptor should be empty and rate limiting service should not be called. Logs should not show any log from the limitador service or GRPC client.

[eguzki]

requires https://github.com/Kuadrant/wasm-test-framework/pull/2

[eguzki]

ready for review @alexsnaps