fix(js): Fix hierarchy and examples for sample rate configuration

[mydea]

This PR improves the "Tracing > Configure Sampling" page in two main ways:

1. It introduces proper headings for the two main sections - this way, you can link there, and it makes more sense structurally IMHO.
2. It fixes the tracesSampler examples - you should always use inheritOrSampleWith for the default sample rate, otherwise you break propagation. We need to make sure to use this consistently in examples!

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[codecov]

Bundle Report

Changes will decrease total bundle size by 15 bytes (-0.0%) ⬇️. This is within the configured threshold ✅

Detailed changes

Bundle name	Size	Change
sentry-docs-server-cjs	10.6MB	-9 bytes (-0.0%) ⬇️
sentry-docs-client-array-push	9.44MB	-6 bytes (-0.0%) ⬇️

Affected Assets, Files, and Routes:

view changes for bundle: sentry-docs-server-cjs

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
1729.js	-3 bytes	1.58MB	-0.0%
../instrumentation.js	-3 bytes	910.48kB	-0.0%
9523.js	-3 bytes	886.53kB	-0.0%

view changes for bundle: sentry-docs-client-array-push

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
static/chunks/pages/_app-*.js	-3 bytes	869.55kB	-0.0%
static/chunks/4612-*.js	-3 bytes	398.04kB	-0.0%
static/QFDAQijuVOsf829PkGbiC/_buildManifest.js (New)	578 bytes	578 bytes	100.0% 🚀
static/QFDAQijuVOsf829PkGbiC/_ssgManifest.js (New)	77 bytes	77 bytes	100.0% 🚀
static/YSFqs7Z_VFtrtAhNLHlnO/_buildManifest.js (Deleted)	-578 bytes	0 bytes	-100.0% 🗑️
static/YSFqs7Z_VFtrtAhNLHlnO/_ssgManifest.js (Deleted)	-77 bytes	0 bytes	-100.0% 🗑️

[codyde]

One thing im wondering, based on the feedback from the other Python PR, is if we should actually be changing the language of this section to suggest you can configure "A" traceSampler function; instead of implying this is a function we provide.

The way it was written originally def implies that its a function we give - which isnt the case if I understand right - but that might also be an unnecessary detail. What do you think?

[mydea]

Yeah, that may make sense 🤔 IMHO we can still merge this PR and tweak the exact language we use in a follow up?

[codyde]

Yup - im good with that.