Replace BSTooltip with GlTooltip in app/assets/javascripts/boards/mixins/sortable_default_options.js

What does this MR do?

Replaces BSTooltip with GlTooltip in app/assets/javascripts/boards/mixins/sortable_default_options.js

Testing

1. Go to a board
2. Put two issues in the same panel column
3. Give one of the issues a due date in the future
4. Hover over the due date in the board issue, see the tooltip show (see screenshot below)
5. Drag the issue
6. The tooltip should disappear while dragging, and re-appear after drag is released

Screenshots

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 #249795 (closed)