feat(relay): add span-normalization.allowed-hosts into relay config

[aldy505]

Complementary relay config for getsentry/relay#3813, based on the discussion on getsentry/relay#3572

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Look, I get it. The entity doing business as "Sentry" was incorporated in the State of Delaware in 2015 as Functional Software, Inc. and is gonna need some rights from me in order to utilize my contributions in this here PR. So here's the deal: I retain all rights, title and interest in and to my contributions, and by keeping this boilerplate intact I confirm that Sentry can use, modify, copy, and redistribute my contributions, under Sentry's choice of terms.

[aldy505]

/cc @jjbayer

[jjbayer]

We also need to register the option, see for example

sentry/src/sentry/options/defaults.py

Lines 2347 to 2354 in 23ccc70

	# list of platform names for which we allow using unsampled profiles for the purpose
	# of improving profile (function) metrics
	register(
	"profiling.profile_metrics.unsampled_profiles.platforms",
	type=Sequence,
	default=[],
	flags=FLAG_ALLOW_EMPTY | FLAG_AUTOMATOR_MODIFIABLE,
	)

[aldy505]

Hey @jjbayer is there anything else that's blocking this PR? Since not all checks are green.