docs(metrics): align headings of Metrics usage

[Flash0ver]

DESCRIBE YOUR PR

During #16054, I notice that the headings of platform-includes/metrics/usage/* are not aligned across all platforms:

• H3: JavaScript, Java (Document Java Metrics #16032)
• H2: PHP, Python, Ruby

Question: Do we want to do this?
Alternatively, we could change it to H4, so that they don't show up in the hierarchy like for "Options".

from -> to

IS YOUR CHANGE URGENT?

Help us prioritize incoming PRs by letting us know when the change needs to go live.

• Urgent deadline (GA date, etc.):
• Other deadline:
• None: Not urgent, can wait up to 1 week+

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 added an urgent due date to it.
  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

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Review	Updated (UTC)
sentry-docs	Ready	Preview, Comment	Jan 16, 2026 9:08pm

1 Skipped Deployment

Project	Deployment	Review	Updated (UTC)
develop-docs	Ignored		Jan 16, 2026 9:08pm