Update log string encode

[waynesun09]

Encode the string with utf-8 and ignore error

[waynesun09]

@kkaarreell RP operation team got user report with 504 response, and from postgres DB log it's the log table with the message encoding issue, you have raised PR:
#3092

which should cover it but it still exist, so add the encode with utf-8 and decode back before send to the API request.
Could you help check and maybe test from tmt side.

Thanks