feat: show holidays and colour code in attendance calendar (backport #1595)

[mergify]

Description: Show holidays and colour code for each employee in attendance calendar

Before:

After:

Closes #1311 Closes #1173
no-docs (does not require docs as its just a visual enhancement)

---

This is an automatic backport of pull request #1595 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of c82d9a4 has failed:

On branch mergify/bp/version-15-hotfix/pr-1595
Your branch is ahead of 'origin/version-15-hotfix' by 3 commits.
  (use "git push" to publish your local commits)

You are currently cherry-picking commit c82d9a40e.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   hrms/hr/doctype/attendance/attendance.json

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[frappe-pr-bot]

🎉 This PR is included in version 15.17.0 🎉

The release is available on GitHub release

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