feat(flags): Add flags context

[cmanallen]

Adds a new feature context. The goal is to normalize contexts with the key "flags" and the body:

{
    "flags": {
        "values": [
            {"flag": "abc", "result": true}
        ]
    }
}

Where result is any valid JSON value.

[Dav1dde]

Please add documentation for all types and fields. This is not just internal but also used to generate our official event schema, having these fields documented doesn't just help Relay development but also SDK developers.

[cmanallen]

@Dav1dde Added documentation and integration test coverage.

[cmanallen]

@Dav1dde While writing the coverage for a malformed flags context I noticed relay doesn't reject the envelope but instead forwards the flags context as an empty object (aside from the type key). Is this intentional behavior so we reject fewer envelopes?

[Dav1dde]

So relay should just forward all contexts it does not know untouched but PII scrubbed.

This variant of the enum is supposed to ensure this:

    /// Additional arbitrary fields for forwards compatibility.
    #[metastructure(fallback_variant)]
    Other(#[metastructure(pii = "true")] Object<Value>),

If that is not the case (turned into an empty object) and you have a testcase to repro, please open a new issue/bug and we'll have to fix that. That should definitely not be the case.

---

If you mean in the flags context, I think you'd have to explicitly add an other field, like there is e.g. in the GpuContext:

    /// Additional arbitrary fields for forwards compatibility.
    #[metastructure(additional_properties, retain = true, pii = "maybe")]
    pub other: Object<Value>,

Good catch, I missed that, we probably should have that on every struct in the context (well up to you, it's forward compatibility).

[Dav1dde]

@Dav1dde Added documentation and integration test coverage.

Nice thanks, that stuff is really helpful not just for testing but also potential regressions.