fix: res.send of cy.intercept doesn't override json-related content types

[flotwig]

Reverts #17400

Re-adds #17199

Closes #17084

User facing changelog

res.send of cy.intercept doesn't override json-related content types.

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[flotwig]

@sainthkh this was causing a CI failure in develop that looks legitimate, can you please take a look at the review comments on this PR and resolve them?

[cypress]

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Test summary

8359 • 0 • 103 • 3 • 4

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Run details

Project	cypress
Status	Passed
Commit	dd7c3af
Started	Aug 6, 2021 12:24 AM
Ended	Aug 6, 2021 12:35 AM
Duration	10:22 💡
OS	Linux Debian - 10.8
Browser	Multiple

View run in Cypress Dashboard ➡️

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Flakiness

	commands/net_stubbing_spec.ts		1
1	network stubbing > intercepting request > can intercept utf-8 request bodies without crashing
	commands/xhr_spec.js		1
1	src/cy/commands/xhr > abort > aborts xhrs currently in flight
	cypress/proxy-logging-spec.ts		2
1	Proxy Logging > request logging > fetch log shows resource type, url, method, and status code and has expected snapshots and consoleProps
2	Proxy Logging > request logging > fetch log shows resource type, url, method, and status code and has expected snapshots and consoleProps

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