docs(js): Update the OpenTelemetry pages for v11, keep v10 versions

[JPeer264]

DESCRIBE YOUR PR

closes SDK-1351

Every page in the OpenTelemetry section documented APIs that v11 removed:

• skipOpenTelemetrySetup was replaced by enableOpenTelemetrySetup.
• SentryContextManager, SentrySampler, SentrySpanProcessor and
  validateOpenTelemetrySetup were removed, so wiring Sentry's
  components into a provider you own is no longer possible.
• The openTelemetryInstrumentations and openTelemetrySpanProcessors
  options were removed.

Snapshot all three pages as __v10.x so readers on v10 keep working
instructions, since every one of those APIs is valid there, and rewrite
the current pages around what v11 ships.

• The landing page claimed OpenTelemetry instrumentation is picked up
  "without any further configuration". It isn't: the SDK registers no
  tracer provider by default, so spans from @opentelemetry/api are not
  captured. Describe the two ways to connect the pipelines instead.
• "Using Your Existing OpenTelemetry Setup" was built end to end on the
  removed components. It now covers the two setups that exist, and says
  what happened to the components it used to document.
• "Using OpenTelemetry APIs" loses the two sections built on the removed
  options. Adding instrumentation goes through OpenTelemetry's own
  registerInstrumentations(), and the page states that it assumes
  enableOpenTelemetrySetup: true.

The performance/opentelemetry-setup includes are left alone: only the v10 page renders them now, and they document v10 correctly.

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Select exactly one option. For deadlines, replace YYYY-MM-DD with the due date. You can update this information later by editing the PR description.

• Urgent deadline (GA date, etc.): YYYY-MM-DD
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SLA

• Teamwork makes the dream work, so please add a reviewer to your PRs.
• Please give the docs team up to 1 week to review your PR unless you've supplied a deadline.

Thanks in advance for your help!

PRE-MERGE CHECKLIST

Make sure you've checked the following before merging your changes:

• Checked Vercel preview for correctness, including links
• PR was reviewed and approved by any necessary SMEs (subject matter experts)
• PR was reviewed and approved by a member of the Sentry docs team

LEGAL BOILERPLATE

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.

EXTRA RESOURCES

• Sentry Docs contributor guide

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[linear-code]

SDK-1351

[github-actions]

Please update the IS YOUR CHANGE URGENT? section of the PR description:

• Select exactly one option.
• If you selected an urgent or other deadline, provide the date as YYYY-MM-DD.

This information helps the Docs team prioritize your review.

[sentry]

Bug: The v10 documentation snapshot custom-setup__v10.x.mdx contains an empty <Alert> block, which will render a confusing, empty box for users viewing v10-specific documentation.
_{Severity: LOW}

Suggested Fix

Restore the original content about 'lightweight mode' inside the <Alert> block within the custom-setup__v10.x.mdx file. This will ensure the v10 documentation snapshot is complete and provides the necessary context for users.

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/javascript/common/opentelemetry/custom-setup__v10.x.mdx#L119

Potential issue: The documentation snapshot for v10, `custom-setup__v10.x.mdx`, contains
an empty `<Alert>` block. This block was intended to preserve content about 'lightweight
mode' for users of the v10 SDK. Instead, it will render a visually empty and confusing
alert box for users viewing the v10 documentation for specific platforms like Node,
Express, and others. While this does not cause a functional failure in the SDK, it
creates a regression in documentation quality and leaves v10 users without important
guidance that was supposed to be preserved.

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

[msonnb]

superseded by #19458