[expo-cli] Add a eas:build:init command

[satya164]

Why

We want to add a separate command to configure the project for eas builds without having to actually start a build.

Test plan

Run expo eas:build:init in a project. I had some issues with generating credentials on iOS but it's unrelated to this PR as I haven't changed any logic for credentials.

[wkozyra95]

I'm not convinced that we should support options like profile and platform.
If this command is intended be ran only once we should setup both platforms and preferably default build profile
If we want to support running android and ios config separately we should modify eas.json if it exists.

@dsokal what do you think?

[dsokal]

I think I failed to communicate what needs to be done here, sorry. Here are the requirements:

• Ideally, expo eas:build:init should be run only once in the lifespan of the project. Because the EAS Builds commands shouldn't be visible for our users yet, I've implemented a kinda feature flag for them. Check out this if - https://github.com/expo/expo-cli/blob/master/packages/expo-cli/src/commands/eas-build/index.ts#L9 We want to streamline the process of setting up EAS Builds (creating eas.json and configuring project before build) thus the need for this command. This command should create eas.json if it doesn't exist yet. We want to make this new command available to users without having eas.json but we don't want to list it in the help output. Regarding the latter part, I'm not sure if it's feasible with our version of commander so we may need to implement some hack.
• expo eas:build:init should set up both Android and iOS projects by default -> no need for the platform parameter.
• I think there is no need for the profile param. The configuration phase seems unrelated to build profiles.
• expo eas:build should check whether the project is configured and if it's not it should print an error saying that expo eas:build:init should be run first. For Android, we can grep the project for the apply from: "./eas-build.gradle" line. For iOS, I think we can always run the autoconfiguration steps.

[dsokal]

Looks good, please update the changelog! :)

[wkozyra95]

Also, remember to update documentation here https://github.com/expo/expo/tree/master/docs/pages/build

[dsokal]

Also, remember to update documentation here https://github.com/expo/expo/tree/master/docs/pages/build

Yeah, actually please open a PR to docs before merging this.
#2442 - please update the docs for this feature too

[wkozyra95]

Also, remember to update documentation here https://github.com/expo/expo/tree/master/docs/pages/build

Yeah, actually please open a PR to docs before merging this.
#2442 - please update the docs for this feature too

We talked offline with dominik and we think that it's better to merge it earlier, just make sure that docs are ready before expo-cli is published.