BRE2-976: allow setting of launchable parameters

[drewmalin]

Allow launchable parameters to be set:

Missing parms:

❯ ./brev create -l env-3Ge8dxSYkYLewLVDsNhKAmEiVDD
Deploying launchable: "fancy parms"
Instance type: n2d-highcpu-2
Storage: 256
Build mode: VM
Required Parameters:
    B
    D    (allowed: aaa, bbb, ccc)
Optional Parameters:
    A    (default: default)
    C    (allowed: 123, 456, 789; default: 456)

invalid launchable parameters:
  - missing required parameter "B"; provide --param B=VALUE
  - missing required parameter "D"; provide --param D=VALUE

Invalid value:

❯ ./brev create -l env-3Ge8dxSYkYLewLVDsNhKAmEiVDD --param B=hi --param D=a
Deploying launchable: "fancy parms"
Instance type: n2d-highcpu-2
Storage: 256
Build mode: VM
Required Parameters:
    B
    D    (allowed: aaa, bbb, ccc)
Optional Parameters:
    A    (default: default)
    C    (allowed: 123, 456, 789; default: 456)

invalid launchable parameters:
  - invalid value "a" for "D" (allowed: aaa, bbb, ccc)

Unknown parameter:

❯ ./brev create -l env-3Ge8dxSYkYLewLVDsNhKAmEiVDD --param B=hi --param D=aaa --param E=aaa
Deploying launchable: "fancy parms"
Instance type: n2d-highcpu-2
Storage: 256
Build mode: VM
Required Parameters:
    B
    D    (allowed: aaa, bbb, ccc)
Optional Parameters:
    A    (default: default)
    C    (allowed: 123, 456, 789; default: 456)

invalid launchable parameters:
  - unknown parameter "E"