fix #2190: Base64 encode SMBIOS value strings in order to allow more characters

fix #2190: Base64 encode SMBIOS value strings in order to allow more characters

On some occasions e.g. license checking, the manufacturer string in the
SMBIOS settings edit has to allow characters such as whitespaces.
https://forum.proxmox.com/threads/proxmox-and-windows-rok-license-for-dell.53236/
In principle SMBIOS allows to pass any zero terminated string to the
corresponding fields in the structure type 1 (System Information).

By base64 encoding the values clashing of the config is avoided.

Relies on the corresponding patch to pve-manager to obtain base64 encoded values.

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>