Show one digit after dot in commit_per_day value in charts page.

What does this MR do?

This MR adds functionality to show fractions of commit_per_day on repository/charts page (ie. https://gitlab.com/msdundar/gitlab-ce/graphs/master/charts)- as suggested by @dzaporozhets on #26512 (closed).

Examples:

actual value	before	after
0.21	0	0.2
0.02	0	0.0
5	5	5.0
5.4132	5	5.4

Why was this MR needed?

• An average value doesn't need to be an integer, it can also be a float too.
• Showing a value such as 0.5 commits_per_day is more meaningful than showing 0 commits per day for a repository with commits.
• This change was requested in #26512 (closed).

Screenshots (if relevant)

Before:

After:

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conforms to the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

#26512 (closed).