proposal: add new type measurement unit (MB/GB/TB)

nginx conf support measurement units like `1024`, `8KB`, `1MB`) see [http://nginx.org/en/docs/syntax.html](http://nginx.org/en/docs/syntax.html) but hcl does not now.

Wish we can support the measurement unit type in HCL:)

The issue does not name any files, tests, or entry points, and only proposes adding measurement units such as MB, GB, and TB to HCL. First determine how HCL represents numeric literals and where its grammar and type system are defined. Done would require an agreed unit representation, parsing behavior, and tests for the proposed syntax.

Written by the indexing model from the issue text.