feat(elixir): Add propagator, LiveView tracing, and Plug.Telemetry note

[sl0thentr0py]

DESCRIBE YOUR PR

Document Sentry.OpenTelemetry.Propagator for distributed tracing via sentry-trace and baggage headers. Add LiveView trace propagation setup using LiveViewPropagator and Plug.LiveViewContext. Include note about OpentelemetryPhoenix requiring Plug.Telemetry in the endpoint.

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Project	Deployment	Actions	Updated (UTC)
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[sentry]

Bug: The documentation for text_map_propagators suggests a mixed list of atoms and module references, a pattern not confirmed to be supported by the OpenTelemetry Elixir SDK.
_{Severity: MEDIUM}

Suggested Fix

Verify with the OpenTelemetry Elixir SDK source code or official documentation whether mixed-type lists are supported for text_map_propagators. If not, update the documentation to show a supported configuration pattern, which might involve using only atoms or providing a different mechanism for custom propagators.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent.
Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not
valid.

Location: docs/platforms/elixir/tracing/index.mdx#L65-L70

Potential issue: The documentation suggests configuring `text_map_propagators` with a
mixed list containing both atoms (e.g., `:trace_context`) and module references (e.g.,
`Sentry.OpenTelemetry.Propagator`). There is no authoritative documentation or source
code evidence from the OpenTelemetry Elixir SDK to confirm that it can parse and handle
such a mixed-type list. If a user implements this configuration, the application could
either crash during initialization or, more subtly, fail to register the custom
propagator, leading to incomplete tracing data in production without any obvious error.

_{Did we get this right? 👍 / 👎 to inform future reviews.}

[sl0thentr0py]

@solnic is this a valid problem?