Improve Issue Board's horizontal space usage

What does this MR do?

I changed and added some CSS rules to improve the way Issue Boards use the horizontal space.

There is no functional code involved and automatic test are not required.

Applying this changes we can also reduce the impact of the issue reported by @blackst0ne: #22933 (moved) improving UX

This is an actual screen I took for POC:

Let's compare:

Off course, it is responsive too:

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance 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

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 #60485 (moved)