Add --rate-limit flag

[paschun]

Add the rate limit flag like in binstall

It's needed for binaries hosted on gitlab, otherwise get slammed with http code 429 "rate limit exceeded"
Thus currently can only use binstall for binaries on gitlab, can't use cargo-update.

      --rate-limit <RATE_LIMIT>
          Override the rate limit duration.
          
          By default, cargo-binstall allows one request per 10 ms.
          
          Example:
          
          - `6`: Set the duration to 6ms, allows one request per 6 ms.
          
          - `6/2`: Set the duration to 6ms and request_count to 2, allows 2 requests per 6ms.
          
          Both duration and request count must not be 0.
          
          [env: BINSTALL_RATE_LIMIT=]
          [default: 10/1]

[nabijaczleweli]

Is there any particular reason you can't set BINSTALL_RATE_LIMIT?

[paschun]

Yes, the env variable works too. Thank you