Onboarding checklist and form V1

[jakecosgrove]

Description

This PR:

• adds a new page /onboard-with-nhs-notify to /get-started
• changes the layout of the /get-started page to include the side navigation
• introduces the /onboard-with-nhs-notify in the /get-started page
• links to the 'confirm your setup' form that integrators need fill to get access to our integration environment

Context

The /onboard-with-nhs-notify page is designed to:

• set expectations for prospects before they engage with NHS Notify and register their interest
• help integrators to progress their integration by giving them guidance on what they need to do, in what order and when
• remove the need for integrators to seek additional support from the onboarding team

Type of changes

• Refactoring (non-breaking change)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would change existing functionality)
• Bug fix (non-breaking change which fixes an issue)

Checklist

• I am familiar with the contributing guidelines
• I have followed the code style of the project
• I have added tests to cover my changes
• I have updated the documentation accordingly
• This PR is a result of pair or mob programming

---

Sensitive Information Declaration

To ensure the utmost confidentiality and protect your and others privacy, we kindly ask you to NOT including PII (Personal Identifiable Information) / PID (Personal Identifiable Data) or any other sensitive data in this PR (Pull Request) and the codebase changes. We will remove any PR that do contain any sensitive information. We really appreciate your cooperation in this matter.

• I confirm that neither PII/PID nor sensitive data are included in this PR and the codebase changes.

[emmagifford]

Happy to approve!

• new side nav layout in /get-started works correctly
• minor update to the use case section, as requested by Emily, looks fine
• checked /onboard-with-nhs-notify against our Confluence draft - all looks good, links work correctly

Spotted a couple of tiny style changes (setup needs changing to set up and I need to add a couple of links to the Sandbox environment and API and MESH docs) but I'll fix those when I do my next PR on Monday.