fix config issue with tags

[ssoroka]

resolves #8417

[Quinteger]

Hey, was this commit included into the 1.17 release?
Still getting the same issue while trying to configure Jolokia2 agent.

[prajsree]

Hi,

should we include "tag_rename" also to the ignore list ?.

The below configuration was giving an error for me.

[[processors.regex]]
  [[processors.regex.tag_rename]]
    pattern = "^tags_(.*)$"
    replacement = "${1}"

2021-12-13T19:25:49Z E! [telegraf] Error running agent: Error loading config file conf/telegraf_inbuilt.conf: plugin processors.regex: line 58: configuration specified the fields ["tag_rename"], but they weren't used

Adding the tag_rename to the ignore list in missingTomlField seems to be solving this error