Rename the dotenv binary to dotenv-rust

I've updated the rules file for dotenv to rename the binary to dotenv-rust. Similar logic in fd-find was used as a template, as suggested in !41 (comment 95614).

I can build this locally, but get the following lintian output:

E: rust-dotenv changes: bad-distribution-in-changes-file UNRELEASED-FIXME-AUTOGENERATED-DEBCARGO
W: rust-dotenv source: changelog-should-mention-nmu
W: rust-dotenv source: source-nmu-has-incorrect-version-number 0.14.1-1
W: dotenv: new-package-should-close-itp-bug
W: dotenv: binary-without-manpage usr/bin/dotenv-rust
W: librust-dotenv-dev: new-package-should-close-itp-bug

I wasn't able to figure out how to get rid of W: dotenv: binary-without-manpage usr/bin/dotenv-rust, as trying to direct the help2man output to debian/dotenv-rust.1 (instead of debian/dotenv.1) resulted in a build error. I wasn't able to find an example in this repo that renames a binary and generates a man page to use as guidance.

I don't think I need to worry about any of the other lintian output at this stage, but let me know if there is anything else I can do to help there.

merged

mentioned in commit 79ad81e0