Please check if the PR fulfills these requirements

• The PR has no duplicates (please search among the Pull Requests
  before creating one)
• The PR follows
  our contributing guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• UPGRADING.md has been updated with a migration guide (for breaking changes)

• What kind of change does this PR introduce?

Changes all occurences of the term telemetry to metrics.

• What is the current behavior?

No behaviour changed.

• What is the new behavior?

Same as before.

• Does this PR introduce a breaking change, and is titled accordingly?

Yes, the UPGRADING.md file has been updated accordingly.

• Other information:

None.

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