Add option to change cgroup root path (enhanced recording)

[gabrielcorado]

Closes #36304. Enables users to configure the directory used to store cgroup sessions.

Example with multiple agents per node

Two services configured with:

# teleport-1.yaml
ssh_service:
  enabled: "yes"
  enhanced_recording:
    enabled: true
    root_path: /agent-1

# teleport-2.yaml
ssh_service:
  enabled: "yes"
  enhanced_recording:
    enabled: true
    root_path: /agent-2

The structure is different for each:

$ ls /cgroup/agent-1/
1441b074-e6c1-4918-9b4c-43f13864308b  cgroup.threads         cpu.stat         memory.events        memory.stat
cgroup.controllers                    cgroup.type            cpu.uclamp.max   memory.events.local  memory.swap.current
cgroup.events                         cpu.idle               cpu.uclamp.min   memory.high          memory.swap.events
cgroup.freeze                         cpu.max                cpu.weight       memory.low           memory.swap.high
cgroup.kill                           cpu.max.burst          cpu.weight.nice  memory.max           memory.swap.max
cgroup.max.depth                      cpu.pressure           io.max           memory.min           memory.zswap.current
cgroup.max.descendants                cpuset.cpus            io.pressure      memory.numa_stat     memory.zswap.max
cgroup.pressure                       cpuset.cpus.effective  io.prio.class    memory.oom.group     pids.current
cgroup.procs                          cpuset.cpus.partition  io.stat          memory.peak          pids.events
cgroup.stat                           cpuset.mems            io.weight        memory.pressure      pids.max
cgroup.subtree_control                cpuset.mems.effective  memory.current   memory.reclaim       pids.peak

$ ls /cgroup/agent-2/
7968061b-1f4a-40bd-abff-065acd783ae3  cgroup.type            cpu.uclamp.min                        memory.high          memory.swap.high
cgroup.controllers                    cpu.idle               cpu.weight                            memory.low           memory.swap.max
cgroup.events                         cpu.max                cpu.weight.nice                       memory.max           memory.zswap.current
cgroup.freeze                         cpu.max.burst          fc9a493b-aa66-4154-896a-99e80fa182e6  memory.min           memory.zswap.max
cgroup.kill                           cpu.pressure           io.max                                memory.numa_stat     pids.current
cgroup.max.depth                      cpuset.cpus            io.pressure                           memory.oom.group     pids.events
cgroup.max.descendants                cpuset.cpus.effective  io.prio.class                         memory.peak          pids.max
cgroup.pressure                       cpuset.cpus.partition  io.stat                               memory.pressure      pids.peak
cgroup.procs                          cpuset.mems            io.weight                             memory.reclaim
cgroup.stat                           cpuset.mems.effective  memory.current                        memory.stat
cgroup.subtree_control                cpu.stat               memory.events                         memory.swap.current
cgroup.threads                        cpu.uclamp.max         memory.events.local                   memory.swap.events

Check on the session itself:

# SSH using Agent 1
$ tsh ssh root@agent-1
$ cat /proc/$$/cgroup
0::/agent-1/1441b074-e6c1-4918-9b4c-43f13864308b/113e8528-ce12-46cf-b637-de2f200523d8

# SSH using Agent 2
$ tsh ssh root@agent-2
$ cat /proc/$$/cgroup
0::/agent-2/7968061b-1f4a-40bd-abff-065acd783ae3/82ba74f1-9413-4e9d-b276-bf4929d76a45

---

changelog: Add ssh_service.enhanced_recording.root_path configuration option to change the cgroup slice path used by the agent.

[zmb3]

Looks good. Don't forget docs updates.

[public-teleport-github-review-bot]

@gabrielcorado See the table below for backport results.

Branch	Result
branch/v13	Create PR
branch/v14	Create PR
branch/v15	Create PR