Add "jekyll" label to .asf.yaml

[niallkp]

Platforms affected

N/A

Motivation and Context

Adding the jekyll label so that its easier to find ASF projects using Jekyll

(I've created an Infra PR to add this GitHub Query to the Infra Project Website page)

Description

Add "jekyll" label to .asf.yaml

Testing

N/A

Checklist

• [ N/A] I've run the tests to see all new and existing tests pass
• [ N/A] I added automated test coverage as appropriate for this change
• [ N/A] Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• [ N/A] If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary