Add an optional parameter to enforce a specific vendor

[ldeso]

The use case would be to block the installation of toolchains from vendors that are not trusted.

For example, this could be useful if one wants to build a Gradle project from some source code that is not audited, and only trusts a specific vendor. In that case, setting this optional parameter would guarantee that no toolchain will be downloaded and installed from any other vendor than the trusted one.

Looking at the source code, it seems that this feature could be implemented in the file FoojayToolchainResolver.kt, by checking that the vendor obtained from spec.vendor.get() matches the one specified by the optional parameter.