Add option --bin for choosing one binary when there are more than one binaries

[wzhd]

A beginner in esp decided to build several slightly different binaries by placing the source codes in src/bin in the same project. The following error message is produced when the binary to flash is not specified:

 Error: cargo_espflash::multiple_artifacts
 
   × Failed to build project
   ╰─▶ Multiple build artifacts found
  help: Please specify which artifact to flash using --bin

Running cargo espflash --bin myapp1 /dev/ttyACM0 doesn't seem to solve it, though, with this message:

error: Found argument '--bin' which wasn't expected, or isn't valid in this context

      If you tried to supply `--bin` as a value rather than a flag, use `-- --bin`

This commit adds the option --bin to build_options, which has worked in my case.

[jessebraham]

Good catch, thank you for fixing this! I've relaxed the Clippy checks a bit on master since this has been opened so I won't worry about the failing check in this PR, it's a pretty silly reason.

Just one final thing before I merge, we are in the process of trying to re-license this project to MIT/Apache 2. Assuming you consent to your contributions being under these licenses rather than GPL2 could you please just say so in this RFC?

EDIT: the re-licensing has completed, so I hope you're okay with that as I'm going to go ahead and merge this 😁