[DOCS] Salt Cloud documentation overhaul

[dwoz]

Summary

Comprehensive refresh of the Salt Cloud documentation, addressing 9 docs / docs-with-code issues across the cloud driver suite.

• New canonical reference page (doc/topics/cloud/events.rst) listing every event tag emitted by Salt Cloud (lifecycle, power-state, reactor-hook, and per-resource events). The Salt Master Events page and the reactor tutorial cross-link to it. ([DOCS] Inconsistent documentation of cloud events #64629, partial [DOCS] Inconsistent documentation of cloud options #65063)
• Cloud writers' guide: drop the "script() is required" language (salt.utils.cloud.bootstrap() does the work) and replace the stale Linode-as-libcloud-example with CloudStack / Dimension Data. ([DOCS] salt-cloud script() function should not be listed as required #65323, [DOCS] Extending Salt Cloud - outdated example of module that is using libcloud #58719)
• OpenNebula create() docstring: drop the misleading salt-cloud -p ... memory=... cpu=... vcpu=... example (those positional args get treated as additional VM names) and document the workaround. ([DOCS] OpenNebula Function Reference - Suggests wrong CLI syntax #64520)
• EC2 register_image: full kwarg reference plus a multi-volume block_device_mapping CLI example that survives the shell parser. ([DOCS] salt-cloud and register_image function #60679)
• VMware: documented customization_spec (was completely absent from the docs) and added a Known Issues section pointing at the Ubuntu hostname-not-set bug ([DOCS] customization_spec is missing from the VMware cloud docs #57933, [salt-cloud] [vmware] issue setting hostname on ubuntu  #55889).
• AzureARM: documented bootstrap_interface and the fact that the generic ssh_interface / win_interface options are not consulted by this driver; added notes referencing the make-master traceback ([BUG] Creating a salt-master vm on azurearm fails #58096) and the list index out of range query error ([BUG][SALT][CLOUD][OPTIONS] There was a query error: list index out of range #65064). ([DOCS] Inconsistent documentation of cloud options #65063)
• SoftLayer: added .. deprecated:: 3006.0 banners on both softlayer and softlayer_hw (driver source + Getting Started page). (Softlayer cloud module scheduled deprecation and deletion #56546)

Tests

• tests/pytests/unit/cloud/test_cloud_events_documented.py — scans salt/cloud/clouds/, salt/cloud/__init__.py, and salt/utils/cloud.py for cloud.fire_event tag literals, normalises them, and asserts each appears on the new reference page. Future drivers that introduce a new tag will fail this test until the doc is updated.
• tests/pytests/unit/cloud/clouds/test_opennebula_options.py, test_ec2_options.py, test_vmware_options.py, test_azurearm_options.py, test_softlayer_options.py — docstring / doc-page tracking tests that hold each driver's user-facing documentation accountable for the runtime behaviour described in the code.

All 516 cloud unit tests pass; sphinx-build -W -b html produces no warnings.

Issues fixed

• Softlayer cloud module scheduled deprecation and deletion #56546
• [DOCS] customization_spec is missing from the VMware cloud docs #57933
• [BUG] Creating a salt-master vm on azurearm fails #58096
• [DOCS] Extending Salt Cloud - outdated example of module that is using libcloud #58719
• [DOCS] salt-cloud and register_image function #60679
• [DOCS] OpenNebula Function Reference - Suggests wrong CLI syntax #64520
• [DOCS] Inconsistent documentation of cloud events #64629
• [DOCS] Inconsistent documentation of cloud options #65063
• [BUG][SALT][CLOUD][OPTIONS] There was a query error: list index out of range #65064
• [DOCS] salt-cloud script() function should not be listed as required #65323

Branch strategy

3006.x first. Cloud drivers no longer exist on 3008.x / master (the directory was emptied in 3008.0 except for saltify), so the merge-forward bot will carry the changes that still apply forward to 3007.x and stop there. The reactor / events reference pages live in doc/topics/cloud/ which still exists on 3008.x and master; those will follow naturally during merge-forward.

Test plan

• pytest tests/pytests/unit/cloud/ — 516 passed, 4 skipped
• sphinx-build -W -b html — clean
• pre-commit run --files <touched> — clean (auto-format applied)