Update meters.md

[clalissayi24]

Added new Pay as you go meter (fourth meter for SPE)

Category

• Content fix
• New article

Related issues

• fixes #issuenumber
• partially #issuenumber
• mentioned in #issuenumber

What's in this Pull Request?

Adding details around a new fourth meter - Pay as you go messages. This explains SPE agents - what meter it uses and the cost. Note: I am intentionally NOT including the link to Copilot studio meter and breakdown of different meter costs because in the same document, it references PPAC enablement and setting up PAYG in PPAC, which will be very confusing for our users.

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[learn-build-service-prod]

Learn Build status updates of commit b91ac51:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/embedded/administration/billing/meters.md	✅Succeeded	View

For more details, please refer to the build report.

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