fix: set projectId in a custom config file

[elevatebart]

• Closes cypress open - new projectId creation not respecting --config-file #5747

User facing changelog

When using a custom config file and setting up its connection to the dashboard, Cypress now writes the projectId in the custom config file instead of cypress.json.

To test

Create a project with a custom.json file as the configuration

yarn install
yarn start --project=/path/to/the/project --config-file=custom.json

Then open the runs tab

Finally, connect the current project with the Cypress cloud

PR Tasks

• Have tests been added/updated?
• Has the original issue or this PR been tagged with a release in ZenHub?

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[cypress]

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Test summary

18502 • 0 • 214 • 7 • 2

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Run details

Project	cypress
Status	Passed
Commit	f54deca
Started	Sep 27, 2021 1:53 PM
Ended	Sep 27, 2021 2:03 PM
Duration	10:27 💡
OS	Linux Debian - 10.9
Browser	Multiple

View run in Cypress Dashboard ➡️

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Flakiness

	cypress/proxy-logging-spec.ts		1
1	... > works with forceNetworkError
	e2e/redirects_spec.js		1
1	redirection > meta > binds to the new page after a timeout

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[jennifer-shehane]

Nice and thanks for the writeup on how to test the feature manually. I manually tested and it looks good. Tests updated as well.