Document how to use `INIT_` values for customizing init experience

UDS CLI includes a number of special `INIT_` values that can be used to customize the init experience for a bundle. These values can configure the registry, git experience, etc and may be necessary in some environments.

Definition of done: New how-to guide on the docs website that covers how to provide these custom init values when deploying a bundle.

Note: This is possible using special `UDS_` envs or the uds-config file. Examples should be provided for both.

Start by locating the docs website and existing guidance for bundle deployment, then identify how the special INIT_ values are described alongside the UDS_ environment variables and uds-config file. Done means a new how-to guide explains both ways to provide custom init values, with examples for each.

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