paramiko_ssh_runner: add pubkey certificates

[freddierice]

Implements feature #6346, adding support for SSH Certificate Signing.

[CLAassistant]

All committers have signed the CLA.

[danxg87]

@fdrab it appears unit tests are all failing with the following:

ProcessExecutionFailure: Process 'Building pytest.pex' failed with exit code 1.
stdout:

stderr:
There was 1 error downloading required artifacts:
1. st2-rbac-backend 3.9.dev0 from git+https://github.com/StackStorm/st2-rbac-backend.git@master
    Expected sha256 hash of e49a85b9d1ad7cd9e75d53810ddf1e3ec50c83b1e4d8629d80f0566a233e5637 when downloading st2-rbac-backend but hashed to d34d5cbb539182553ec8b35a0763decb6b66bd37aa51f3a61db1eb30449f6f10.

is there something we need to update on our end (besides adding an entry to CHANGELOG.rst @freddierice )

[freddierice]

I got as much green as possible by:

• running pants fmt ::
• bumping the hash on the new st2-rbac-backend (master will continue to change over time)

The last tests are failing due to functionality that is unrelated to this PR.

[danxg87]

@fdrab any input here as to the remaining failing tests?
https://github.com/StackStorm/st2/actions/runs/17077003546/job/48420931756?pr=6347#step:9:82
https://github.com/StackStorm/st2/actions/runs/17077003546/job/48420931776?pr=6347#step:9:37
https://github.com/StackStorm/st2/actions/runs/17077003546/job/48420931816?pr=6347#step:8:141

These do not appear to be related to this change?

[fdrab]

Hi. I'm not a maintainer / reviewer. I usually ignore errors that are obviously not related to the changes I've made, as the testing framework and some other components may be WIP.

[danxg87]

Hi. I'm not a maintainer / reviewer. I usually ignore errors that are obviously not related to the changes I've made, as the testing framework and some other components may be WIP.

OH! Sorry about that haha. Thanks for the heads up on the tests. I will try to poke a reviewer/maintainer on this.