Resolve "Support custom text for coverage badges"

What does this MR do?

• Allow to pass a key_text query parameter to a badge URL to customize the key text
• Allow to pass a key_width query parameter to a badge URL to customize width of the key box
• Add calculation of the box width based on the string width using ttfunk apparently ttfunk has a GPL license, which is not an acceptable license for GitLab. I added a character width lookup hash instead

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

Relates to #17555 (closed)