[v0.10] [SURE-9010] Backport of Gitjob pod cannot create known_hosts, read-only filesystem

[manno]

Backport of #2826

[mmartin24]

This issue seems fixed in Rancher v2.9-08f6f0d7cfc29882892c19b8ebc56e9c9568dd58-head with fleet fleet-agent:v0.10.2-rc.4

• Able to create knownhost_file as described in https://fleet.rancher.io/gitrepo-add#known-hosts and correctly seen in UI:
  

• Able to access the following private gitrepo and deploy nginx image without errors with this file:

URL: git@github.com:fleetqa/fleet-qa-examples.git
Branch: main
Path: nginx