vault-cli: create a new moudle that installs vault CLI in a workspace and puts it in the PATH

[matifali]

Currently, we install vault CLI as part of our other vault modules. Let us create a new module that only installs the vault CLI without the authentication steps.

It should be an easy lift as we have all the installation-related code in all vault modules.

Part of #49

[moo-im-a-cow]

my PR for making the token optional in the vault-token module would mean that module can be used to install vault without attempting any authentication,
then it should be usable to install the vault cli as part of the other vault modules

#90

[matifali]

Thanks @moo-im-a-cow. The purpose of this issue was to refactor and extract all that functionality into a single module that all other vault modules could use. We have plenty of them now: https://registry.coder.com/modules?tag=vault