User page [1] - Bootstrap User page

[machadoum]

original issue

Describe the feature:
Create a user page copying the Host page layout. Add the page to the menu, breadcrumbs, and top bar navigation. Hide this feature behind a feature flag.

Describe a specific use case for the feature:

• Create the page
• Copy Hosts page layout
• Add it to the Menu below Hosts.
• Make sure breadcrumbs are working
• Make sure the page is accessible on the global search bar.
• Create a feature flag to hide the page

What is not included:

• Page content, tables, and KPIs.

[elasticmachine]

Pinging @elastic/security-threat-hunting (Team:Threat Hunting)