Adds the ability to configure the secret key size generated.

[jwoertink]

Purpose

Fixes #1847

Description

This allows you to pass an optional argument to the lucky gen.secret_key task to generate larger or smaller secret keys.

❯ lucky gen.secret_key
jyy8PODnOkPBUKVFd8pxM4YFbxyYTzYK44QoMiha+68=

❯ lucky gen.secret_key -n 64
uOBfVEGWo+t14g7F9vDA349b2OTURQAMfM13VeiMswNsd0YA0oykDP4XEzJcEjTk3PNV8KuiLwAMV4Vg7EhU3A==

Checklist

• - An issue already exists detailing the issue/or feature request that this PR fixes
• - All specs are formatted with crystal tool format spec src
• - Inline documentation has been added and/or updated
• - Lucky builds on docker with ./script/setup
• - All builds and specs pass on docker with ./script/test