Add forward-slash as illegal character in prometheus

[uepoch]

They are considered as an illegal character in prometheus text-format in metrics_name

Example file

TEST[promtheus]$ cat test.txt 
# HELP vault_audit_file/_log_request vault_audit_file/_log_request
# TYPE vault_audit_file/_log_request summary
vault_audit_file/_log_request{quantile="0.5"} NaN
vault_audit_file/_log_request{quantile="0.9"} NaN
vault_audit_file/_log_request{quantile="0.99"} NaN
vault_audit_file/_log_request_sum 1.7049709558486938
vault_audit_file/_log_request_count 1
TEST[promtheus]$ cat test.txt | ./promtool check metrics
error while linting: text format parsing error in line 1: invalid metric name in comment
TEST[promtheus]$ cat test.txt | sed 's#/#_#g' | ./promtool check metrics && echo $?
0

[uepoch]

Hello, sorry for highlighting you @banks, you seem to be the one merging PR for a while.
Can you take a look at this review when you have some time ? We need it for hashicorp/vault#5308
Thanks a lot in advance !

[banks]

Thanks for showing your rationale with promtool.

This seems reasonable to me if Prometheus chokes on these anyway!

[uepoch]

Thanks !