fix(propagation): filter out unsupported dd_origin values

[nirrattner]

We ran into situations where public clients were sending HTTP requests with unsupported non-ascii characters in the x-datadog-origin headers. These headers were being propagated, via the HTTPPropagator.extract and gRPC client interceptor, to branching gRPC calls. The gRPC calls are then failing on the client side due to gRPC client side validation which forbids metadata values with non-ascii characters.

The proposed solution here will prevent these unsupported headers values from being propagated by preventing them from being set within Context. This approach may impact HTTP propagation to branching HTTP requests, but my understanding is that non-ascii characters are not supported in these situations either.

Checklist

• Change(s) are motivated and described in the PR description.
• Testing strategy is described if automated tests are not included in the PR.
• Risk is outlined (performance impact, potential for breakage, maintainability, etc).
• Change is maintainable (easy to change, telemetry, documentation).
• Library release note guidelines are followed. If no release note is required, add label changelog/no-changelog.
• Documentation is included (in-code, generated user docs, public corp docs).
• Backport labels are set (if applicable)

Reviewer Checklist

• Title is accurate.
• No unnecessary changes are introduced.
• Description motivates each change.
• Avoids breaking API changes unless absolutely necessary.
• Testing strategy adequately addresses listed risk(s).
• Change is maintainable (easy to change, telemetry, documentation).
• Release note makes sense to a user of the library.
• Reviewer has explicitly acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment.
• Backport labels are set in a manner that is consistent with the release branch maintenance policy
• If this PR touches code that signs or publishes builds or packages, or handles credentials of any kind, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.

[pr-commenter]

Benchmarks

Benchmark execution time: 2023-09-07 21:26:01

Comparing candidate commit 9bb2043 in PR branch nirrattner/dd-origin-supported-characters with baseline commit 6fa9b0e in branch 1.x.

Found 2 performance improvements and 0 performance regressions! Performance is the same for 102 metrics, 0 unstable metrics.

scenario:flasksimple-tracer

• 🟩 execution_time [-330.554µs; -278.202µs] or [-5.263%; -4.429%]

scenario:sethttpmeta-useragentvariant_not_exists_2

• 🟩 max_rss_usage [-895.057KB; -681.493KB] or [-3.106%; -2.365%]