Add an actions menu to the metrics dashboard header

What does this MR do?

Adds an actions menu to the metrics dashboard header.

For this MVP, the actions menu will contain actions to

• Create new dashboard
• Duplicate current dashboard (only when viewing the default dashboard)

The menu button will show a tooltip when hovered.

The "Create new" action

• Opens up a modal
• The modal contains a link to the project URL and a link to the documentation related to creating YML dashboards
• The documentation link opens in a new tab

The "Duplicate dashboard" action

• Is present only when the default dashboard is opened
• Is an exact duplicate of the "Duplicate dashboard" already present in the dashboards dropdown

Related issue: #223204 (closed)

Screenshots

The "Actions menu" in context of the default dashboard

It contains a Duplicate dashboard action:

The "Actions menu" in context of a custom dashboard

Doesn't contain a Duplicate dashboard action:

The "Create new" modal

Video

Screen_Recording_2020-06-30_at_12.24.09

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team