feat(decl): add process test resource and kill system call test step

[ekoops]

What type of PR is this?

Uncomment one (or more) /kind <> lines:

/kind bug

/kind cleanup

/kind documentation

/kind tests

/kind feature

Any specific area of the project related to this PR?

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/area commands

/area pkg

/area events

What this PR does / why we need it:
This PR introduces the process test resource and the kill system call test step. The process test resources is required to test the rules involving processes manipulation, such as killing a process or tracing it. The code for creating a configurable process has been exported in a separate package process, and it is leveraged by the host runner and the process resource. Moreover, this PR fixes some minor style issues.

The following is a yaml sample to test the behaviour:

tests:
  - name: test_kill_and_process_res
    rule: "-"
    description: "Testing kill system call and process resource"
    runner: HostRunner
    resources:
      - type: process
        name: p1
    before: |
      echo "Beginning test..."
    steps:
      - type: syscall
        name: k1
        syscall: kill
        args:
          pid: "${p1.pid}"
          sig: SIGKILL
    after: |
      echo "Test ended"

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ekoops, leogr

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[poiana]

LGTM label has been added.

Git tree hash: a2624c88cc6e292476c137e9c1fb25bbce596395

[leogr]

/hold

[leogr]

/unhold