all: upgrade minimum supported Go release to 1.22

[nsrip-dd]

What does this PR do?

With Go 1.23 released on 2024-08-13, we drop support for Go 1.21. This
means Go 1.22 is now our minimum supported Go release. Update our CI
files to reflect our current supported Go versions, and remove pre-Go
1.22 workarounds.

In addition to the CI bumps, this PR changes/fixes a few things related to the upgrade:

• Drops the old rand from the tracer, now that we can depend on math/rand/v2.
• Uses slices in the appsec package.
• The TestWrapHandlerWithResourceNameNoRace got a new data race. Specifically,
  by bumping our go.mod to 1.22, we get the new 1.22 ServeMux behavior internally.
  The 1.22 ServeMux modifies the Request, introducing a race with all the goroutines
  accessing/modifying the request concurrently. Fix it by giving each goroutine its own
  request. I verified that the test still catches the intended bug by reverting the fix from
  contrib/net/http: Copy span options and resource name to avoid data race #2204 and verifying that the test fails.

Motivation

Follow our declared Go support policy.

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.
• Add an appropriate team label so this PR gets put in the right place for the release notes.
• Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.

Unsure? Have a question? Request a review!

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-09-09 17:01:02

Comparing candidate commit 333ddfe in PR branch nick.ripley/go-122-minimum with baseline commit c29e8fa in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 58 metrics, 1 unstable metrics.

[darccio]

LGTM

[eliottness]

I believe there are small changes to do here

[nsrip-dd]

I believe there are small changes to do here

Done, thanks for the review @eliottness