diff: Diff metrics even if tags changed

[matthiasbeyer]

I would like to be able to diff metrics even if their tags changed.

For example:

1. I have a metrics "binary-size" that has a tag "rustc-version: 1.90.0"
2. I have a new metrics "binary-size" but it does not have "rustc-version: 1.90.0" but "rustc-version: 1.92.0"

When using git metrics diff on those, they are different metrics:

- binary-size{rustc.version="1.90.0"} 29719480.00                                                                                                                                                                                                                                                                                                                                                                                         
+ binary-size{rustc.version="1.90.0"} 29576360.00 (-0.48 %)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
+ binary-size{rustc.version="1.92.0"} 29644072.00                                                                                                                                                                                                                                                                                                                                                                                         

but (IMO) there should be an option to diff them and ignore the tags, so the output is then:

- binary-size{rustc.version="1.90.0"} 29719480.00                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
+ binary-size{rustc.version="1.90.0" -> "1.92.0"} 29644072.00 (<something> %)

Would be nice to have a flag for that.