Add getBy docs pages

[ankur22]

What?

This adds docs pages for the following APIs:

• page.getByRole
• page.getByAltText
• page.getByLabel
• page.getByPlaceholder
• page.getByTitle
• page.getByTestId
• page.getByText

Checklist

• I have used a meaningful title for the PR.
• I have described the changes I've made in the "What?" section above.
• I have performed a self-review of my changes.
• I have run the npm start command locally and verified that the changes look good.

• I have made my changes in the docs/sources/k6/next folder of the documentation.

Related PR(s)/Issue(s)

Check links in description.

[mstoykov]

Please add

{{< code >}}

<!-- md-k6:skip -->

before and

{{< /code >}}

After all the code examples that won't run.

[heitortsergent]

Suggested change

	### Returns
	### Returns

Is this following the same pattern as other pages? It looks like we could move the headings up for all of these (from h3 to h2, etc.)

[ankur22]

I think we have this issue in most of the browser docs (maybe elsewhere too) where the heading is one level too low. Would you rather I fix all of them in a new PR?

[heitortsergent]

Just to clarify, we don't need to use the {{ < code > }} if we have a code block for one language. We only need to use it if we want to show a code example in multiple languages, and to have the tabbed feature on that code block. We have an example here.

[ankur22]

Just to clarify, we don't need to use the {{ < code > }} if we have a code block for one language. We only need to use it if we want to show a code example in multiple languages, and to have the tabbed feature on that code block. We have an example here.

Thanks for clarifying! I was wondering whether I needed them or not. When I remove them, then can i still work with <!-- md-k6:skip --> and <!-- eslint-skip -->?

EDIT: Yep, those directives still work without the {{< code >}}, so i'll remove them to avoid confusion in the future.