Integrate this project into the main server

[SchoolGuy]

As a developer
I want be able to not maintain duplicated code in relation to distro_signatures.json
so that I can take advantage of the advanced functionality of this library in the main server.

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Some remarks for this issue:

• If there are changes required to this library to make access for consumers of the library easier, let's discuss it and do it, we haven't tagged anything yet
• The CLI of this library needs to be mature enough to work with existing distro_signatures.json files
• The serialization for the server items we need to adjust since that is at the moment storing the strings for the versions. If we switch to the DAO (data access objects) here, then we need to be careful with serialization and the XML-RPC API.

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My idea for the timeline is the following:

• This project is being integrated into the main server codebase in a pre-release (let's say something alike 0.1.0)
• We test everything before a Cobbler release
• We iterate the first two points before this one until we are happy with the results
• We tag 1.0.0 for this library
• We upgrade the Cobbler dependency to 1.0.0
• We release Cobbler with the integrated library

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Code usages I was able to identify:

• https://github.com/cobbler/cobbler/blob/0ea84602160b0216d0bd641789dc42885ffb352d/cobbler/api.py#L174-L189
• https://github.com/cobbler/cobbler/blob/0ea84602160b0216d0bd641789dc42885ffb352d/cobbler/api.py#L1548-L1587
• https://github.com/cobbler/cobbler/blob/0ea84602160b0216d0bd641789dc42885ffb352d/cobbler/remote.py#L2729-L2739
• https://github.com/cobbler/cobbler/blob/0ea84602160b0216d0bd641789dc42885ffb352d/cobbler/modules/managers/import_signatures.py#L311-L370
• https://github.com/cobbler/cobbler/blob/0ea84602160b0216d0bd641789dc42885ffb352d/cobbler/utils/signatures.py
• https://github.com/cobbler/cobbler/blob/0ea84602160b0216d0bd641789dc42885ffb352d/cobbler/validate.py#L233-L288

Additionally the CLI has some usages but we ignore those as we will not put effort into a deprecated CLI. The effort needs to be put into the Golang CLI. This CLI can be progressed as soon as cobbler/cobbler#3164 (with PR cobbler/cobbler#3244) is fixed (merged) and we have merged cobbler/cobblerclient#10 on the CLI.