Support EC keys for VaaS

[angelmoo]

Now VaaS support generating certificates using EC keys, and creating CIT that accepts EC keys.

for requesting a CIT or updating a CIT:

{
"keyTypes": [
{
"keyType": "RSA",
"keyLengths": [
1024,
2048,
3072,
4096
]
},
{
"keyType": "EC",
"keyCurves": [
"P256",
"P384",
"P521",
"ED25519"
]
}
],

and for requesting a certificate:

{
"csrAttributes": {
"keyTypeParameters": {
"keyType": "EC",
"keyLength": null,
"keyCurve": "P256"
}

Chages are needed on Vcert to support these new behavior.