Improve metric "issue size"

[LucPrestin]

As a user, I'd like to have a meaningful metric for issue sizes to that I can really compare two or more issues.

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💭   Hints & Thoughts

Currently the issue size is measured be the amount of characters in the issue body. This does not have any semantic meaning though. Issue size really means the complexity of the issue. This metric should reflect that too.

❓   Additional Questions to Answer / Consider

What is a good metric for the complexity of an issue?

• number of characters in the issue body?
• number of checkboxes in issue body?
• number of images?

[chrisma]

Most likely a combination of the listed factors could be used. It's important to be clear on the display page how this score was calculated.