docs(rum): document the axios integration for HarmonyOS

[Fiona2016]

The HarmonyOS network section described two integration paths and pointed everyone else at getHeaders(). That call returns trace headers but no way to report the resource, so axios users — the largest group the two paths do not cover — had to assemble the resource lifecycle themselves and get the sampling flag, the span id encoding and the first-party gate right on their own.

SDK 0.4.0 ships @flashcatcloud/axios, and FlashcatTrace.startTracedResource() for stacks without a dedicated package.

Changes

• The network section opens with a table mapping each network library to its integration, then covers all four: rcp interceptor, FlashcatHttp, axios, and anything else.
• New axios section: install @flashcatcloud/axios, call trackAxios(instance). Warns that interceptors are per-instance and must be registered exactly once.
• New other network stacks section for startTracedResource(), including the two things a caller still owns — passing the full url, and closing the resource on the failure path.
• The consent / first-party / existing-traceparent note now states it applies to all four paths, rather than reading as specific to FlashcatHttp.
• data-collection lists the two new ways a resource can be produced, and separates the four that need setTrackNetworkRequests(true) from the manual API that does not.
• Module versions move to 0.4.0, with @flashcatcloud/axios in the install snippet marked as needed only by axios users.

The 0.3.2 on the advanced-config page is left alone — it dates a behaviour change rather than naming the current release.

mint broken-links passes. zh and en updated together.

Note: 0.4.0 is submitted to the registry and awaiting review, so hold this until the packages are live.