Feat(eos_designs): Enhance isis authentication support

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The more I read the more I think we will need to revisit all this ISIS authentication at some point:

It seems today in eos_designs we only support this TOI: https://www.arista.com/en/support/toi/eos-4-15-2f/13687-isis-md5
our keys are not able to discriminate between levels from eos_designs
There is no mention of using SHA which is described here (and supported by our filters): cf this TOI: https://www.arista.com/en/support/toi/eos-4-21-3f/14126-is-is-authentication-using-sha
and recently this was introduced with shared-secret: https://www.arista.com/en/support/toi/eos-4-30-0f/17486-support-for-hitless-authentication-key-rollover-for-is-is
[interesting recommendation]: To maximize interoperability, Arista recommends using the same key in both interface mode and in the router isis mode.

[!NOTE] eos_cli_config_gen supports all this.

Research direction: Study the existing ISIS authentication implementation in eos designs, review the provided TOI links for MD5, SHA, and shared secret authentication, and identify where level discrimination and SHA support are missing.
Tech stack: python
Domain: backend
Issue type: Feature
Difficulty: 3
Estimated time: 1-2 days
Activity status: Active
Clarity: Clear
Prerequisites: PythonGit
Newbie friendliness: 60