Fix enterprise downloads

[drewmullen]

HashiCorp has started hosting enterprise binaries on the same page as oss downloads (example link). Due to this change the download function of your script was failing for enterprise. This PR fixes it. There are other improvements that could be made. its likely the download_oss and download_enterprise functions could be combined but i didnt want to refactor too much

Changes:

• include new VAULT_ENT_TYPE to specify which enterprise binary to get
• remove unnecessary VAULT_FILE
• add the individual vault file to the unzip command. the enterprise zip has many more files that are likely unnecessary for testing purposes

I tested with

EDITION=oss
PLATFORM=arm64

and

EDITION=enterprise
VAULT_ENT=1.21.1
PLATFORM=arm64
VAULT_ENT_TYPE=ent

[drewmullen]

also - question... any qualms if i update the script to work with a newer version of vault by default in a future PR? I believe this will require some changes to the default vault config file

sent this up as a 2nd pr in case theres a reason to not upgrade: #908