Add more actions to and change UI of dashboard actions menu

What does this MR do?

Changes the monitor dashboard actions menu as described in #228856 (closed)

Description

• move "Star dashboard", "Add metric" and "Edit dashboard" inside of the actions menu
• conditionally show and/or display a disabled (i.e. greyed out) state for some items in the actions menu based on the current dashboard being OOTB or custom
• replace the current icon of the actions menu with a hamburger icon

Action menu item states

These are the states of the actions menu items based on whether the current dashboard is OOTB or custom.

Item	Rendered	Disabled	Observations
Add metric	OOTB	n/a
Edit dashboard YAML	OOTB/Custom	OOTB	This is rendered but disabled in OOTB in order to entice users to create a new dashboard and edit it
Duplicate current dashboard	OOTB	n/a	In the future the Custom dashboards will also be duplicatable
Star dashboard	OOTB/Custom	n/a	Text toggles between Star dashboard / Unstar dashboard
Create new dashboard	OOTB/Custom	n/a

Screenshots/videos

OOTB

Before

After

Custom

Before

After

Videos

OOTB dashboard	Custom dashboard
Screen_Recording_2020-08-10_at_03.14.22	Screen_Recording_2020-08-10_at_03.08.11

This an Implementation issue for #220931 (closed). This issue is critical to allow us to implement add data to a custom dashboard, if designs need to be prioritized we should implement the custom dashboard actions first and OOTB dashboard second.

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