CMPT 34053 impove flavors search

[morozovalekseywot]

• Add cpu_generation param to terraform schema of vkcs_compute_flavor
• If you set the min_ram or min_disk parameter and more than one suitable flavor is found in the search result, flavor with minimum of RAM is automatically selected.
• Improve error messages for vkcs_compute_flavor

[morozovalekseywot]

and lets change datasorce example to get STD2 or STD3 flavor there with the same cpu/ram as at the moment

also add an example of searching appropriate flavor by min_ram

add 3 examples, min_ram, min_disk, min_ram + min_disk