qemu_capabilities: Add QEMU_CAPS_DISPLAY_RELOAD

qemu_capabilities: Add QEMU_CAPS_DISPLAY_RELOAD

The 'display-reload' QMP command was introduced in QEMU 6.0.0, so we
add a compatible capability to check if target QEMU binary supports it.

{"execute":"display-reload", "arguments":{"type": "vnc", "tls-certs": true}}

The new QMP refer to:
https://gitlab.com/qemu-project/qemu/-/commit/9cc07651655ee86eca41059f5ead8c4e5607c734

Signed-off-by: Zheng Yan <yanzheng759@huawei.com>
Signed-off-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>