[8.2](backport #31798) [libbeat] Improve syslog parser/processor error handling

[mergify]

This is an automatic backport of pull request #31798 done by Mergify.
Cherry-pick of cabc8ba has failed:

On branch mergify/bp/8.2/pr-31798
Your branch is up to date with 'origin/8.2'.

You are currently cherry-picking commit cabc8badb9.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   CHANGELOG.next.asciidoc
	modified:   NOTICE.txt
	modified:   go.mod
	modified:   go.sum
	modified:   libbeat/processors/syslog/docs/syslog.asciidoc
	modified:   libbeat/processors/syslog/syslog.go
	modified:   libbeat/reader/syslog/docs/syslog.asciidoc
	modified:   libbeat/reader/syslog/parser/common.rl
	modified:   libbeat/reader/syslog/parser/parser_rfc3164.rl
	modified:   libbeat/reader/syslog/parser/parser_rfc5424.rl
	modified:   libbeat/reader/syslog/parser/rfc3164.rl
	modified:   libbeat/reader/syslog/parser/rfc5424.rl
	modified:   libbeat/reader/syslog/rfc3164_gen.go
	modified:   libbeat/reader/syslog/rfc3164_test.go
	modified:   libbeat/reader/syslog/rfc5424_gen.go
	modified:   libbeat/reader/syslog/rfc5424_test.go
	modified:   libbeat/reader/syslog/util.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   libbeat/processors/syslog/syslog_test.go
	both modified:   libbeat/reader/syslog/message.go
	both modified:   libbeat/reader/syslog/message_test.go
	both modified:   libbeat/reader/syslog/syslog.go
	both modified:   libbeat/reader/syslog/syslog_test.go
	both modified:   libbeat/reader/syslog/util_test.go

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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• Start Time: 2022-07-05T16:18:23.595+0000

• Duration: 98 min 1 sec

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[mergify]

This pull request has not been merged yet. Could you please review and merge it @taylor-swanson? 🙏