Add a CLI option to truncate benchmark names

[harendra-kumar]

In results like these:

FileSystem.Handle/o-1-space/copy/read/SS.encodeUtf8 . SS.decodeUtf8Lax (1/10)                                                 950.08                      +0.32
FileSystem.Handle/o-1-space/reduce/toChunks/S.splitOnSeqUtf8 "abcdefgh" FL.drain . US.decodeUtf8ArraysLenient (1/10)           55.84                      +0.29

The benchmark name is too long, we would like to only print the last n characters of the benchmark name based on a CLI option, where n comes from the CLI option.

[harendra-kumar]

@specdrake would you like to try this.