feat(disk): add IOPS limiters.

[Zenithar]

What does this PR do?

• Adds new functionality
• Alters existing functionality
• Fixes a bug
• Improves documentation or testing

Extends the DiskPressure disruption with IOPS throttling support alongside the existing bandwidth (bytes/sec) throttling.

Changes

API (api/v1beta1/disk_pressure.go)

• Add readIOPSPerSec and writeIOPSPerSec fields to DiskPressureThrottlingSpec
• Validate all throttle fields are non-negative (zero = remove limit; negative = rejected at admission)
• Extend GenerateArgs() to emit --read-iops-per-sec / --write-iops-per-sec flags
• Extend Explain() with IOPS descriptions

Injector (injector/disk_pressure.go)

• Rename diskPressureThrottleModeRead/Write → diskPressureThrottleModeReadBps/WriteBps to disambiguate from new IOPS modes
• Add diskPressureThrottleModeReadIops / diskPressureThrottleModeWriteIops enum values
• cgroups v1: write to blkio.throttle.read_iops_device / blkio.throttle.write_iops_device
• cgroups v2: write riops= / wiops= key-value pairs to the unified io.max file
• Inject() and Clean() handle all four throttle modes
• Add IopsKey observability tag for structured logging

CLI (cli/injector/disk_pressure.go)

• Wire --read-iops-per-sec / --write-iops-per-sec flags

Docs & Examples

• Update docs/disk_pressure.md and docs/disruption_catalogue.md
• Add examples/disk_pressure_read_iops.yaml example manifest
• Update examples/complete.yaml

CRDs

• Regenerated chaos.datadoghq.com_disruptions.yaml, _disruptioncrons.yaml, _disruptionrollouts.yaml

Code Quality Checklist

• The documentation is up to date.
• My code is sufficiently commented and passes continuous integration checks.
• I have signed my commit (see Contributing Docs).

Testing

• I leveraged continuous integration testing
  • by depending on existing unit tests or end-to-end tests.
  • by adding new unit tests or end-to-end tests.
• I manually tested the following steps:
  • Inject readIOPSPerSec on a cgroups v1 node → verify blkio.throttle.read_iops_device written
  • Inject writeIOPSPerSec on a cgroups v2 node → verify io.max contains wiops=
  • Cleanup path resets all four throttle files to 0
  • locally.
  • as a canary deployment to a cluster.

[datadog-prod-us1-5]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 62.96%
• Overall Coverage: 39.24% (+0.26%)

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