New component: Add systemd receiver

[Hemansh31]

The purpose and use-cases of the new component

The systemd receiver collects the value of different properties of a systemd unit and publishes that data as metrics data.

Example configuration for the component

receivers:
systemd:
services:
- sshd.service
- example.service
properties:
- ActiveState
- LoadedState
- MainPID

Telemetry data types supported

These would be primarily metrics

Is this a vendor-specific component?

• This is a vendor-specific component
• If this is a vendor-specific component, I am a member of the OpenTelemetry organization.
• If this is a vendor-specific component, I am proposing to contribute and support it as a representative of the vendor.

Code Owner(s)

@Hemansh31

Sponsor (optional)

@atoulme

Additional context

No response

[atoulme]

Can you share what metadata.yaml would look like?

[Hemansh31]

type: systemdunitsreceiver
scope_name: otelcol/systemdunitsreceiver


attributes:
  name:
    description: Name of the systemd unit.
    type: string

  type:
    description: The type of systemd unit.
    type: string
    enum: [service, timer, target, socket, mount]
  
  pid:
    description: MainPID of the systemd unit
    type: int


# ActiveState Code
# Value   Meaning   Description
#   0   active        unit is ~
#   1   reloading     unit is ~
#   2   inactive      unit is ~
#   3   failed        unit is ~
#   4   activating    unit is ~
#   5   deactivating  unit is ~


# LoadState Code
# Value   Meaning   Description
#   0   loaded        unit is ~
#   1   stub          unit is ~
#   2   not-found     unit is ~
#   3   bad-setting   unit is ~
#   4   error         unit is ~
#   5   merged        unit is ~
#   6   masked        unit is ~

metrics:
  systemd.service.ActiveState:
    enabled: true
    description: Active State of the systemd service.
    unit: ~
    gauge:
      value_type: int
    attributes: [name, type, pid]
  systemd.service.LoadState:
    enabled: true
    description: Load State of the systemd service.
    unit: ~
    gauge:
      value_type: int
    attributes: [name, type, pid]

[Hemansh31]

Can you share what metadata.yaml would look like?

@atoulme shared metadata.yml for systemd unit file receiver, this is just a reference of what the metadata.yml would look like, will need to do some modifications upon design finalization

[atoulme]

I am interested in sponsoring this component.

[Hemansh31]

Thanks @atoulme, will start working on the PR for this component. I am following the guidelines specified here, do let me know if I am missing something