Feature Request - expression lang support

[nmnellis]

Use case: I am currently reporting the http path of each request to prometheus for monitoring. I noticed that the path contains the query parameters as well. i would like to remove the query parameters from the http path label.

On a more general level it would be nice to use expressions to parse the data being sent to a given adapter.

[douglas-reid]

From the attribute vocab definition:

request.path | string | The HTTP URL path including query string

We should consider the introduction of a new "standard" attribute with query string removed. This can be used as a compliment to the pending api mgmt work as well.

adding a substring type of func to the expression language is also a path forward here.