[processor/tailsampling] Drop policy type

[portertech]

Description

This pull-request introduces a new policy type to explicitly drop traces regardless of other policy decisions. The new drop policy type behaves much like an and, however, it returns a Dropped decision when all of its policies return Sampled. A Dropped decision takes precedence over all others. The Dropped decision is not new, however, it was unused and therefor safe to use for this purpose. This new policy type is very approachable and capable.

This new policy type can be used to replace the top-level (not within an and policy) use of invert_match to control the final sampling decision. We could deprecate the current invert_match top-level decision logic. The string, numeric, and boolean filter policies still support invert_match, which continues to flip the decision for the individual policy. Let invert_match be simple.

Example:

{
    name: drop-it-like-its-hot,
    type: drop,
    drop: {
        drop_sub_policy: 
        [
            {
                name: do-not-sample,
                type: boolean_attribute,
                boolean_attribute: { key: app.do_not_sample, value: true },
            }
        ]
    }
}

This is a reduced version of a previous PR #37760

Related Issues

• [processor/tailsampling] Allow invert matches in composite policy to continue processing #36673
• [processor/tailsampling] invert_match not given precedence when inside and policy #33656
• Tail-based sampling with policies evaluated with first match mechanism #36795
• [processor/tailsampling] numeric attribute invert match evaluation not prioritized #34296
• [processor/tailsampling] invert_match precedence  #34085
• Unexpected behavior of And policy #29637
• Tail-sampling evaluation completing but not filtering out any traces for Grafana Tempo Distributed  #27049
• Probably more 😅

[atoulme]

You are codeowner of this component.

[jmacd]

LGTM