Angular: Fix handling of docsMode option in angular builder

[ndelangen]

Original PR: #18384

What I did

The docsMode option when using the angular builder had no effect when I tried to build a project using Storybook v6.5.6.
The schema for the builder documents the option with the name docsMode (matching other documentation), however the implementation tries to forward a property with the name docs and ignores the other one.

As the builder also uses the property name docsMode, no further mapping between the two names other than a simple renaming is done in this PR.
Note that the relevant schema part seems to be last updated in #15194, however the implementation was not updated back then.

[ndelangen]

@ssams would love a review on this. 🙏

[ndelangen]

@shilman I'll merge this if it goes green, since you approved the original PR

[ssams]

@ssams would love a review on this.

looks good to me

[tmeasday]

The CLI flag is called --docs-- this documentation was wrong.

[ssams]

The CLI flag is called --docs-- this documentation was wrong.

well, the CLI flag may be called like this, but the Angular builder option certainly is not, Angular wouldn't event allow to run the build when validating the angular.json if using the other name in the current state:

storybook/code/frameworks/angular/src/builders/build-storybook/schema.json

Lines 37 to 41 in 994a26d

	"docsMode": {
	"type": "boolean",
	"description": "Starts Storybook in documentation mode. Learn more about it : https://storybook.js.org/docs/react/writing-docs/build-documentation#preview-storybooks-documentation.",
	"default": false
	},

I've been also using this patch locally applied to the stable v6 versions for months now, so it for sure works with these (e.g. also with currently latest https://github.com/storybookjs/storybook/releases/tag/v6.5.15). When I created the original PR it also fixed everything as intended for the upcoming v7, if it really doesn't anymore then something more in the Storybook builder internals must have changed.