[TASK][Security Serverless]: Add semantic headings to Get Started page

[1Copenut]

Summary

I refactored the Security Serverless "Getting Started" page to use semantic headings instead of P and SPAN tags marked up as headings. This improves the experience for screen reader users and helps us improve our standing against WCAG SC 1.3.1 - Info and Relationships (Level A). Screenshot attached below.

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Related issues

Please see the related issue link below. This issue originated from an accessibility review of the Security Serverless project.

Checklist

Delete any items that are not applicable to this PR.

• Unit or functional tests were updated or added to match the most common scenarios
• Flaky Test Runner was used on any tests changed
• Any UI touched in this PR is usable by keyboard only (learn more about keyboard accessibility)
• Any UI touched in this PR does not create any new axe failures (run axe in browser: FF, Chrome)
• This renders correctly on smaller devices using a responsive layout. (You can test this in your browser)
• This was checked for cross-browser compatibility

For maintainers

• This was checked for breaking API changes and was labeled appropriately

[1Copenut]

Buildkite test this

[elasticmachine]

Pinging @elastic/security-solution (Team: SecuritySolution)

[1Copenut]

Buildkite test this

[angorayc]

Thanks for the enhancement, LGTM

[kibana-ci]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 6289b28

Failed CI Steps

• FTR Configs #12

Test Failures

• [job] [logs] FTR Configs #12 / dashboard app - group 1 dashboard embeddable data grid are added when a cell filter is clicked

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
securitySolution	13.7MB	13.7MB	+198.0B

History

• 💚 Build #206060 succeeded e71dc5b
• 💔 Build #205770 failed 2391f34

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

cc @1Copenut

[1Copenut]

I ran the Flaky Test runner for 10 instances on FTR group 12. All instances passed, so going to merge this item.