Update monitoring with updated grafana metrics view details

[bjormel]

I confirm that this contribution is made under the terms of the license found in the root directory of this repository's source tree and that I have the authority necessary to make this contribution on behalf of its copyright owner.

[Copilot]

Pull request overview

This PR expands the Vespa Cloud monitoring documentation by adding a detailed walkthrough of the METRICS (Grafana) dashboard, including tab-by-tab guidance, annotations, and common troubleshooting workflows.

Changes:

• Added a new “Vespa Cloud metrics dashboard” section describing dashboard structure, tabs/filters, and how to interpret key panels.
• Documented common investigation workflows (latency, feed issues, scaling decisions) to help users navigate from symptoms to root causes.
• Added a new screenshot asset for the “Health Indicators” portion of the Overview tab.

Reviewed changes

Copilot reviewed 1 out of 8 changed files in this pull request and generated 2 comments.

File	Description
en/operations/monitoring.html	Adds extensive new documentation covering the Vespa Cloud metrics dashboard layout, interpretation guidance, and workflows.
assets/img/monitoring-health-indicators.png	Adds a new screenshot referenced by the new “Health Indicators” section.

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[kkraune]

Documentation is great! ideas for later iterations:

• /en/operations/monitoring.html#dashboard-annotations should have links for each item in the table. E.g., the first row should link to en/writing/feed-block.html and so on
• this is great info for operations! in subsequent PRs, we can link to relevant material e.g., for the NN search we have https://vespa-engine.github.io/pyvespa//ann-parameters.html and good blog posts

[kkraune]

💯