Feat: Schedule Activity

[JayDwee]

Summary

Scheduled activities can be set up with k!activity set which can be used for scheduling NUEL final streams

Checklist

• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)

• Have you tested the changes? (pytest & dpytest)
• Have you followed PEP-8 for naming and styling?
• Has your code been properly documented with RestructuredText docstrings?
• Have you added your changes to CHANGELOG.md under the [Unreleased] heading?
• If your code added new bot commands, have you updated documentation.json?

• All of this code is your own, or follows the author repo's licence.

[codecov]

Codecov Report

Merging #298 (0d458aa) into master (c2baf89) will increase coverage by 0.29%.
The diff coverage is 96.81%.

@@            Coverage Diff             @@
##           master     #298      +/-   ##
==========================================
+ Coverage   85.34%   85.64%   +0.29%     
==========================================
  Files         101      107       +6     
  Lines        7302     7488     +186     
==========================================
+ Hits         6232     6413     +181     
- Misses       1070     1075       +5     

Flag	Coverage Δ
unittests	85.64% <96.81%> (+0.29%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
koalabot.py	75.00% <50.00%> (-0.52%)	⬇️
koala/cogs/base/models.py	93.75% <93.75%> (ø)
koala/cogs/base/cog.py	92.36% <96.22%> (+1.56%)	⬆️
koala/cogs/base/core.py	97.29% <97.29%> (ø)
koala/cogs/base/db.py	100.00% <100.00%> (ø)
koala/cogs/base/utils.py	93.33% <100.00%> (-1.91%)	⬇️
koala/db.py	98.91% <100.00%> (+0.13%)	⬆️
tests/cogs/base/conftest.py	100.00% <100.00%> (ø)
tests/cogs/base/test_cog.py	100.00% <100.00%> (ø)
tests/cogs/base/test_core.py	100.00% <100.00%> (ø)
... and 4 more

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[lgtm-com]

This pull request introduces 2 alerts when merging ab64921 into c2baf89 - view on LGTM.com

new alerts:

• 1 for Unused import
• 1 for Module is imported with 'import' and 'import from'

[JayDwee]

merging without review due to fast track

[stefan-cooper]

lgtm :D