Add ADRs for dropping dependency on Kafka

[nscuro]

Description

• Adds "ADR-001: Drop Kafka Dependency"
• Adds "ADR-002: Workflow Orchestration"
• Adds "ADR-003: Notification Publishing"
• Adds "ADR-004: File Storage Plugin"

Addressed Issue

N/A

Additional Details

Refer to the ADRs' contents for details.

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
✅ +18.22% (target: -1.00%)	✅ ∅ (target: 70.00%)

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (31a8525)	201	132	65.67%
Head commit (4b96d85)	6996 (+6795)	5869 (+5737)	83.89% (+18.22%)

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 (#1619)	0	0	∅ (not applicable)

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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