feat(admin): Runtime config notifications take two

[lynnagara]

This PR mostly brings back @MeredithAnya changes from #2185 and cbef1ec

I've adjusted some types and integrated the logging notifier into the create new config API.

[MeredithAnya]

Changes look good to me, thanks for adding those types

[codecov-commenter]

Codecov Report

Merging #2285 (0b2a742) into master (b9f0471) will decrease coverage by 0.12%.
The diff coverage is 58.88%.

@@            Coverage Diff             @@
##           master    #2285      +/-   ##
==========================================
- Coverage   93.06%   92.94%   -0.13%     
==========================================
  Files         553      556       +3     
  Lines       25239    25329      +90     
==========================================
+ Hits        23488    23541      +53     
- Misses       1751     1788      +37     

Impacted Files	Coverage Δ
snuba/admin/notifications/slack/utils.py	25.00% <25.00%> (ø)
snuba/admin/notifications/slack/client.py	41.17% <41.17%> (ø)
snuba/admin/notifications/base.py	75.51% <75.51%> (ø)
snuba/admin/views.py	65.67% <100.00%> (+2.17%)	⬆️

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