Considering improve Error Info on Fixed String Length exceeded

[wey-gu]

For a fresh NG user, when he/she created the very first space and tag and was about to import/insert data. In big chance, the error on VID string exceeded the default max length 8 could be hit, while, the error message is a little bit confusing, as it only refers to the information on only accept int 64 or fixed-length string, where, it's hard to infer on a too short default fixed string length was configured(as the default value).

The expected design will be good to either has information around the actual type of vid(int64 or string with length info) or provide hints on the length limit that was hit. Or, other solutions which could help with this 😁.

Thanks!

[Shylock-Hg]

Had fixed in vesoft-inc/nebula-graph#776