Remove DSS key support from SSH provider for Paramiko 4

[shivaam]

What

This bumps the SSH/SFTP provider Paramiko dependency to Paramiko 4.x and removes Airflow's remaining DSS/DSA key handling paths.

Changes:

• remove paramiko.DSSKey from SSH private-key loading
• reject ssh-dss host keys with a clear migration error
• parse real OpenSSH known_hosts host-key tokens:
  • ssh-rsa
  • ecdsa-sha2-nistp256
  • ecdsa-sha2-nistp384
  • ecdsa-sha2-nistp521
  • ssh-ed25519
• keep bare base64 host_key values as RSA for backward compatibility
• update SSH/SFTP provider docs, README dependency tables, changelogs, and lockfile
• cap Paramiko at <5.0.0 because Paramiko 5 currently breaks existing SSH hook RSA private-key tests

Why

Paramiko 4 removed DSS/DSA support. Airflow was still referencing paramiko.DSSKey, which blocks moving the SSH/SFTP providers to Paramiko 4.

This also avoids a host-key regression: users with a configured ssh-dss host key now get an explicit migration error instead of a raw KeyError, and ECDSA known_hosts values such as ecdsa-sha2-nistp256 ... are parsed with paramiko.ECDSAKey instead of falling through to RSA parsing.

Tests

uv run ruff format providers/ssh/src/airflow/providers/ssh/hooks/ssh.py providers/ssh/tests/unit/ssh/hooks/test_ssh.py
uv run ruff check --fix providers/ssh/src/airflow/providers/ssh/hooks/ssh.py providers/ssh/tests/unit/ssh/hooks/test_ssh.py
uv run --frozen pytest providers/ssh/tests/unit/ssh/hooks/test_ssh.py -q -k 'host_key or dss or unsupported'

Result:

ruff format: 2 files left unchanged
ruff check --fix: All checks passed!
12 passed, 50 deselected, 1 warning

Also ran file-scoped prek validation. All applicable checks passed except Update providers build files, which could not run because Docker was not running locally.

Closes: #54079