Add support for SSH certificate file in Node class

[rnwolfe]

i will fill this out further, but wanted to open PR for viewing outside of myself

Test inclusion requirements

In case the PR contains an enhancement or a new platform/service support, some tests have to be added for the new functionality:

• any fix or enhancement SHOULD include relevant new tests or test updates, if any tests need updating.
• a new platform support MUST include the relevant input files similar to what we have in tests/integration/sqcmds/-input directories, along with the relevant tests in the tests/integration/sqcmds/-samples dir. That list MUST include the all.yml file fully filled out.
• any new service (or table) addition MUST include comments about what network OS are supported (along with version) with this command along with test samples for those platforms and input files in the *-input dir

For additional information about tests, follow this link

Related Issue

Fixes #972

Description

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Type of change

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Adds support for cert-based ssh auth

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

New Behavior

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Contrast to Current Behavior

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Discussion: Benefits and Drawbacks

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Changes to the Documentation

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Proposed Release Note Entry

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Comments

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Double Check

• [x] I have read the comments and followed the CONTRIBUTING.md.
• [x] I have explained my PR according to the information in the comments or in a linked issue.
• [x] My PR source branch is created from the develop branch.
• [x] My PR targets the develop branch.
• [ ] All my commits have --signoff applied

[rnwolfe]

I had rebased my PR on top of #974, so may need to do some git-fu here before merge.

The latest change in https://github.com/rnwolfe/suzieq/commit/6922031bc2db5129db8033ddb74c39a95ac96612 does fix by removing pvt key handling and offloading that to the asyncssh logic which handles it more robustly.

This worked in my environment with ~9 cert-based auth linux nodes.

[rnwolfe]

I ran pytest signed my last commit, but with the other commits I pulled in, I couldn't sign my prior one. I also now added multiple versions of myself to the history. Whoops!

Let me know if I should do anything clean this up.