Add Try-me phase message and New label on landing page with opt out

[jzucadi]

This PR adds a va-alert-expandable component and a "New" label that communicates to landing page users about the MHV to VA.gov transition and helps them understand what exists on VA.gov in this "try me " phase vs. what still remains on MHV classic.

These additions are behind the feature flag: mhvLandingPageEnableVaGovHealthToolsLinks

Related issue(s)

Ticket: https://app.zenhub.com/workspaces/mhv-on-vagov-landing-page-62619a987d74510018ecc546/issues/gh/department-of-veterans-affairs/va.gov-team/81003

Before:

After:

Alert closed

Alert open

Acceptance criteria

• [x] Designed a component that communicates to landing page users about the MHV to VAgov transition and help them understand what exists on VAgov in this "try me " phase vs. what still remains on MHV classic (work with CAIA on content) = Expandable alert from octo: "as a user who is visiting the mhv on va.gov landing page for the first/second time, i want to know what's new on mhv on VAgov and why without having to seek out this information"

• [x] Updated content just below the H1

• [x] Implement design

• [ ] QA review

• [x] A11y review

Quality Assurance & Testing

• [x] I fixed|updated|added unit tests and integration tests for each feature (if applicable).
• [x] No sensitive information (i.e. PII/credentials/internal URLs/etc.) is captured in logging, hardcoded, or specs
• [x] Linting warnings have been addressed
• [x] Documentation has been updated (link to documentation *if necessary)
• [x] Screenshot of the developed feature is added
• [x] Accessibility testing has been performed

Error Handling

• [x] Browser console contains no warnings or errors.
• [x] Events are being sent to the appropriate logging solution
• [x] Feature/bug has a monitor built into Datadog or Grafana (if applicable)