feature(cloud-init): Added the ability to inject extra variables

[Wafffle77]

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Description

Adds the --extra-vars flag to ochami cloud-init group render to allow for injecting key-value pairs into the template renderer. The passed variables can be in any supported input format and can be passed directly, read from a file, or read from stdin.

Implements #82

Type of Change

• New feature

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[synackd]

Thank you for your contribution! I haven't tested this yet but have a couple of initial comments.

[synackd]

We should provide a shorthand if using StringP(), otherwise use String(). I would recommend using e as a shorthand flag here.

Also, the description is a bit long. To avoid too much wrapping, could we shorten it? Something like this to eliminate redundancy: "extra variables to be passed to the template renderer or (if starting with @) file containing extra variables (can be - to read from stdin)"

[synackd]

Since we are adding an extra flag here, we'll want to update the render command in the cloud-init(1) manual page with the flag, following the formatting conventions of the commands around it.