Document the `--ast` flag as an option for `forge build`

[adamegyed]

As of foundry-rs/foundry#7197, the AST is no longer included in the compiler output unless specified with --ast or --build-info. Currently, the --ast flag is undocumented, and should be added to places where it can be specified as an option. This includes forge build, and might include other commands that run forge build internally like forge test or forge script.

[zerosnacks]

Ticket can be closed, this has been fixed as part of the automated workflow introduced in #1135

https://book.getfoundry.sh/reference/cli/forge/build

[zerosnacks]

Marking as resolved