Refactor webhook payload convertion

[lunny]

As title.

[6543]

an it's getting eaven more easyer to add webhooks :)

[codecov-commenter]

Codecov Report

Merging #12310 into master will increase coverage by 0.07%.
The diff coverage is 16.50%.

@@            Coverage Diff             @@
##           master   #12310      +/-   ##
==========================================
+ Coverage   43.32%   43.39%   +0.07%     
==========================================
  Files         646      647       +1     
  Lines       71625    71487     -138     
==========================================
- Hits        31028    31023       -5     
+ Misses      35582    35442     -140     
- Partials     5015     5022       +7     

Impacted Files	Coverage Δ
modules/webhook/discord.go	1.93% <0.00%> (+0.15%)	⬆️
modules/webhook/feishu.go	0.00% <0.00%> (ø)
modules/webhook/msteams.go	0.00% <0.00%> (ø)
modules/webhook/payloader.go	0.00% <0.00%> (ø)
modules/webhook/telegram.go	4.62% <5.55%> (+0.87%)	⬆️
modules/webhook/dingtalk.go	6.81% <6.66%> (+0.84%)	⬆️
modules/webhook/slack.go	30.00% <32.00%> (+2.85%)	⬆️
modules/webhook/matrix.go	34.96% <47.22%> (+4.66%)	⬆️
modules/util/timer.go	42.85% <0.00%> (-42.86%)	⬇️
modules/indexer/stats/db.go	43.47% <0.00%> (-17.40%)	⬇️
... and 13 more

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