[EuiProgress] Add semantic structure to label and value

[myasonik]

Pulling out an idea from PR #3218 into a follow up issue.

Trying to think of a way to join the label and value text so there's something more semantic tying them together rather than just proximity...

I'm thinking maybe a <dl> might work? A DOM structure like this maybe:

<dl>
	<dt>Men's clothing</dt>
	<dd>80%</dd>
	<dd aria-hidden="true"><progress /></dd>
</dl>

If we introduced an extra prop for how to render the wrapping element, we could even extend this to better work with a whole list of these like in the demo. Something like:

<dl>
	<EuiProgress as="div" value={20} label={"Men's clothing"} max={100} />
	<EuiProgress as="div" value={20} label={"Women's clothing"} max={100} />
	<EuiProgress as="div" value={20} label={"Women's shoes"} max={100} />
	<EuiProgress as="div" value={20} label={"Men's shoes"} max={100} />
</dl>

Where as changes the wrapping <dl> of each <EuiProgress /> to a <div> so that we can create one list of progress bars, instead of n lists. (Maybe as is too vague and broad given that <div> is probably the only valid value, but just throwing out an idea.)

[myasonik]

Comments from @cchaos:

I definitely see the benefit of using the <dl> type of structure but it seems way to prescriptive to do this for every single usage.
- What happens if it's just a single progress bar? <dd aria-hidden> doesn't work by itself.
- What if it's only a single use of the progress with a label? Is it ok to have a list with a single item?

Let's consider just making the elements customizable, or we'll need to create a higher component like EuiListGroup that will create the whole element structure.

With the risk of this PR continually expanding greater, let's table this discussion and put it into an issue for follow up.

[myasonik]

What happens if it's just a single progress bar? <dd aria-hidden> doesn't work by itself.

Ah, yeah, you're right. I guess we only go to the <dl> structure if there's a value and label then.

What if it's only a single use of the progress with a label? Is it ok to have a list with a single item?

Yup, should be fine!

[github-actions]

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[daveyholler]

Not planned as the current implementation is acceptable.