Add timeline component

[GuessWhoSamFoo]

What this PR does / why we need it:
Adds a timeline component with support for actions via button group

Which issue(s) this PR fixes

• Fixes Add Timeline component #1064

Special notes for your reviewer:
Helpful boilerplate for setting up a button + timeline:

	bg := component.NewButtonGroup()
	bg.AddButton(component.Button{
		Name:         "testing",
		Payload:      action.Payload{"hello": "world"},
		Confirmation: nil,
		Modal:        component.NewModal(component.Title(component.NewText("test"))),
	})
	steps := []component.TimelineStep{
		{
			State:       component.TimelineStepNotStarted,
			Header:      "Header test",
			Title:       "Title test",
			Description: "Title description",
		},
	}
	timeline := component.NewTimeline(steps, false)
	timeline.Add(component.TimelineStep{
		State:       component.TimelineStepCurrent,
		Header:      "current test",
		Title:       "current title",
		Description: "current description",
		ButtonGroup: bg,
	}, component.TimelineStep{
		State:       component.TimelineStepProcessing,
		Header:      "loading",
		Title:       "loading title",
		Description: "loading description",
	})

[wwitzel3]

We have suggested this before, wondering how you feel about starting with the components we are adding this release.

Add a useful example of using this component to the example plugin? It could be nice show using an action handler to retrigger a specific part of the timeline and having that change the plugin state so that the timeline update starts again...

I'm thinking we can use Sleep calls to simulate the waiting states and an action handler to retry a step.

On first render, the step fails, on retry, set a pass flag, and render the successful timeline.

[wwitzel3]

LGTM

[mklanjsek]

Works well, looks good - nicely done Sam!

[GuessWhoSamFoo]

https://github.com/vmware-tanzu/octant-example-plugins just got an update and will continue to grow in examples moving forward.