Improve Grafana notification tags

[PetrSladek]

Added the ability to set global tags for Grafana annotation and the ability to set tags per Notification with templating capability

[codecov[bot]]

Codecov Report

:x: Patch coverage is 81.25000% with 6 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 55.60%. Comparing base (f485671) to head (c490180). :warning: Report is 17 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/services/grafana.go	79.31%	4 Missing and 2 partials :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #394      +/-   ##
==========================================
+ Coverage   55.35%   55.60%   +0.25%     
==========================================
  Files          35       46      +11     
  Lines        3438     4156     +718     
==========================================
+ Hits         1903     2311     +408     
- Misses       1256     1515     +259     
- Partials      279      330      +51     

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