Change messaging.operation.type=publish to send

[mamwl1]

Fixes #1285

Changes

Change messaging.operation.type=publish to send, as well as the related messaging.client.published.messages metric. Adjust text to use send where appropriate. Update example to use send where appropriate.

Merge requirement checklist

• CONTRIBUTING.md guidelines followed.
• Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
• schema-next.yaml updated with changes to existing conventions.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: lmolkova / name: Liudmila Molkova (eeaffee)
• ✅ login: joaopgrassi / name: Joao Grassi (49d6851)
• ✅ login: mamwl1 / name: MattLeming (9bf4185, ac11be7, c4423d7, a776a21, bd0200c, 2759521, 0c4021b, 7624934, 772cd3f, 45063e8)

[mamwl1]

Closing while CLA is being sorted which might take some time.

[joaopgrassi]

Thank you! I think there are still some "publish" left-overs we need to tackle.

[joaopgrassi]

Heads up: If #1446 merges first, we will need to adapt the new example introduced there.