refactor: combine processMedia and processImage

[MrOrz]

• We will use processImage's logic for images, videos and audios
• refactor(index): replace otherFields with MessageEvent
  • this adds back type and allows narrowing
• feat(processMedia): use media similarity to determine if media is identical

Screenshots

No submission if identical image found

[coveralls]

Pull Request Test Coverage Report for Build 6041476975

• 53 of 62 (85.48%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.3%) to 90.491%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/webhook/handlers/processMedia.ts	42	46	91.3%
src/webhook/index.ts	8	13	61.54%

Files with Coverage Reduction	New Missed Lines	%
src/webhook/index.ts	1	50.0%

Totals
Change from base Build 5892723421:	-0.3%
Covered Lines:	981
Relevant Lines:	1055

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💛 - Coveralls

[MrOrz]

Update after 0831 meeting:

• Show media similarity if available
• More text in option if not displaying thumbnail

• Don't allow sending to DB if options with >=95% media similarity exists