Port: Webhook alert token and new user alerts

[sahibamittal]

Description

This PR adds two new notification types (user_created and user_deleted) and the possibility of setting a token on the webhook alert.

Addressed Issue

Backport change DependencyTrack/hyades#1190

Checklist

• I have read and understand the contributing guidelines
• This PR fixes a defect, and I have provided tests to verify that the fix is effective
• This PR implements an enhancement, and I have provided tests to verify that it works as intended
• This PR introduces changes to the database model, and I have updated the migration changelog accordingly
• This PR introduces new or alters existing behavior, and I have updated the documentation accordingly

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.06% (target: -1.00%)	✅ 93.33% (target: 70.00%)

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (e5ec162)	20203	16451	81.43%
Head commit (a32b45f)	20243 (+40)	16496 (+45)	81.49% (+0.06%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#742)	45	42	93.33%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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