Include values None and 0 for weights in boards scope

What does this MR do?

#11529 (closed)

When setting a new weight for the board scope we are updating the weight attribute of the board and filtering issues when the page reloads. This MR adds the option to persist the values -2, -1 and 0 when selecting weights None, Any and 0 respectively.

Persisted value	Text value	Description
-2	None	Display issues where weight = null
-1	Any	Display issues where weight != null
0	0	Display issues where weight = 0
n	n	Display issues where weight = n

When the weight value is -1 for the board, it displays Any Weight in the field and doesn't include weight in the filter so it includes issues where weight is nil. When filtering by Weight = Any the result will display issues where weight is any value except nil. This behaviour is not consistent but is not modified in this MR as there's an existing issue for it.

Board scope weight = Any Weight	Board weight filter = Any

Screenshots

Screen recording of new behaviour

Screen_Recording_2020-04-15_at_19.27.41

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

Closes #11529 (closed)