Raise the fdlimit if we detect too many open files

[insipx]

This crate: https://github.com/paritytech/fdlimit could help quell the common issue users run into when starting substrate archive for the first time, the too many open files error. This error that occurs as a result of the secondary rocksdb database requiring all files of the primary database to be kept open.

[liuchengxu]

Sounds like we also want to raise a warning like paritytech/substrate#6956?

[insipx]

yeah, a warning with some context would be ideal

[liuchengxu]

@insipx Hi, please take a look at #94, I simply borrowed paritytech/substrate#6956, let me know if you want to display more context.