feat: set default OTel propagator

[guseggert]

This should enable trace context propagation from headers in the HTTP Gateway and APIs.

I think this should have a sharness test to ensure propagation doesn't break, so I'll leave this in draft for now.

Superseds #9180

[BigLep]

@guseggert and @iand : this work and #9169 have beeen open for 6+ months. Is it still relevant?

[guseggert]

This was waiting for bifrost to test this on the gateways but they never finished it that integration. Being able to answer "why was a request slow" or "why did this request time out" seems like a useful thing to have.......

[iand]

Will definitely be useful in Thunderdome

[guseggert]

Yeah maybe we can wire it up in Thunderdome and use that to get this over the line then? Do you have bandwidth for that right now @iand ?

[hacdias]

I repurposed this PR to include ipfs/boxo#256 and the test from #9180. I'll see if the sharness test is properly working, had some issues locally.

[hacdias]

I updated this PR. I think it is ready. Before reviewing, please read ipfs/boxo#256 (comment).

[Jorropo]

I would like to understand what this does, because this isn't setuped yet, however http propagation already works for cmds.

[hacdias]

@Jorropo https://pkg.go.dev/go.opentelemetry.io/contrib/propagators/autoprop@v0.40.0#pkg-overview, for more info ask @guseggert since he added this. AFAIK, the main goal is that it parses the ENV variable and has sensible defaults.

However, it might not make sense since we always use tracing.Propagators() explciitly, so we're never using the default.

[Jorropo]

If we don't use it, I would say let's not do this. Deadcode is bad.

[guseggert]

I'm a little hazy here because this was so long ago, but presumably I was trying to make the propagation user-configurable with OTel standard environment variables. I wouldn't say this is dead code as the intention is to allow users to wire up OTel in their applications, although this could use some tests.

[hacdias]

@guseggert @Jorropo I extracted my commit to #9798.

@guseggert if you want to use autoprop, I think you should either use it as the return value for tracing.Propagators, or set it as default and completely remove tracing.Propagators. But that is not in the scope of what I'm trying to achieve here, so I'll mark this again as a draft.

[hacdias]

Superseded by #9801