feat: expose notification secrets for request payload templating

[eroznik]

Closes #10724

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[eroznik]

Within the related issue, @crenshaw-dev , pointed out that we should be careful to not log this sensitive data. I tried to find a case where this could happen and I didn't find any.
When the notification succeeds, there are no logs with "body". When the notification fails, we get a log with body, but it contains the "template" without the resolved values.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (973565e) 49.55% compared to head (5236341) 49.59%.
Report is 13 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #16055      +/-   ##
==========================================
+ Coverage   49.55%   49.59%   +0.04%     
==========================================
  Files         269      269              
  Lines       46595    46642      +47     
==========================================
+ Hits        23091    23134      +43     
- Misses      21232    21235       +3     
- Partials     2272     2273       +1     

Files	Coverage Δ
util/notification/settings/settings.go	43.47% <100.00%> (+43.47%)	⬆️

... and 10 files with indirect coverage changes

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