Refactor ssh known hosts

[SergK]

EPMDEDP-17256: fix: Verify SSH host keys for all git, GitServer and Gerrit connections

Every outbound SSH connection accepted any host key: the git provider used InsecureIgnoreHostKey for all
repository traffic including the packless transport, the GitServer connectivity check did the same for every
provider, and the Gerrit client used a callback that unconditionally returned nil. A network-position attacker
could impersonate a git server to intercept pushed source or serve falsified refs.

Host keys are now verified against a known_hosts file shipped by the chart as a ConfigMap and mounted as a
directory rather than with subPath, so the kubelet refreshes it in place and added entries take effect without
restarting the operator. The file is seeded with keys for github.com, gitlab.com and bitbucket.org.

In the go-git paths the host key callback is left unset rather than replaced: go-git then derives
HostKeyAlgorithms from known_hosts as well, which avoids spurious key-mismatch failures when a server offers a
key type that is absent from the file.

Failures name the host, the port and the remediation command through GitServer .status.error. A key mismatch is
reported distinctly from an unknown host and never suggests re-scanning, since that would trust whatever key was
just presented.

BREAKING CHANGE: GitServers authenticating over SSH to a host outside the seeded providers must have their host
keys added to knownHosts.entries before upgrading. GitServers using token authentication are unaffected.

Note: git operations for the github, gitlab and bitbucket providers connect on port 22 regardless of
spec.sshPort, so a server on another port needs both entry forms pinned.

[epmd-edp]

Pipeline review-codebase-operator-master-qkvnr ✅ Passed

Status	Task	Duration
✅	github-set-pending-status	6s
✅	fetch-repository	10s
✅	init-values	4s
✅	get-cache	2m6s
✅	commit-validate	5s
✅	dockerfile-lint	7s
✅	helm-lint	5s
✅	helm-docs	10s
✅	build	1m5s
✅	sonar	1m8s
✅	save-cache	1m8s
✅	buildkit-build	29s
✅	github-report-pipeline-status	8s