[Bazel] Update gitignore for bazel-out directory

[lacolaco]

🚀 feature request

Relevant Package

• @angular/bazel

Description

A clear and concise description of the problem or missing capability...

bazel-out directory is created by bazel build but it is not ignored by Git.
It is a compilation output similar to tsc-out.

Describe the solution you'd like

If you have a solution in mind, please describe it.

Update gitignore file for bazel-out directory when ng new --collection=@angular/bazel (or ng add @angular/bazel in the future)

[kyliau]

Similar fix is also in @angular/bazel: https://github.com/angular/angular/blob/master/packages/bazel/src/schematics/ng-add/index.ts#L85-L103

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