fix(outputs.redistimeseries): Handle string fields correctly

[srebhan]

• Updated associated README.md.
• Wrote appropriate unit tests.
• Pull request title or commits are in conventional commit format

resolves #14058

Redis Timeseries do only support numeric field values. Currently, we bluntly send the values to Redis irrespective of their type and receive errors on string fields that convert non-numeric characters. This error then aborts the write and in turn to a retry which will only retrigger the error.

This PR adds a convert_string_fields option which by default tries to convert string-fields to numeric values succeeding if they e.g. contain "3.14" or "0" but failing on any non-convertible values like "3.1.2" or "foo". In the former case the value is sent to Redis while in the latter (failing) case the field is dropped but sending is continued. This resembles the current behavior as close as possible.
When setting the option to false all string fields are dropped and no attempt is made to safe them.

In the course of the PR, we also update the redis client to v9 allowing support for timeseries commands and adding unit tests including a "testcases" framework.

[Hipska]

This PR adds a convert_string_fields option which by default tries to convert string-fields to numeric values succeeding if they e.g. contain "3.14" or "0" but failing on any non-convertible values like "3.1.2" or "foo". In the former case the value is sent to Redis while in the latter (failing) case the field is dropped but sending is continued. This resembles the current behavior as close as possible. When setting the option to false all string fields are dropped and no attempt is made to safe them.

Well, that's a great idea. There are some other outputs that also don't support strings which could benefit from this. A lot of them are just simply dropping any string, regardless of it's value.

[srebhan]

@Hipska feel free to reuse the code!

[Hipska]

Maybe I should list these on a new Issue?

• telegraf/plugins/serializers/graphite/graphite.go

  Lines 157 to 158 in 0c1e213

  	case string:
  	return ""

• telegraf/plugins/serializers/prometheus/convert.go

  Lines 158 to 159 in 0c1e213

  	default:
  	return 0, false

• telegraf/plugins/serializers/wavefront/wavefront.go

  Lines 126 to 128 in 0c1e213

  	case string:
  	// return false but don't log
  	return 0, false

• telegraf/plugins/serializers/splunkmetric/splunkmetric.go

  Lines 193 to 195 in 0c1e213

  	case string:
  	valid = false
  	value = v

• telegraf/plugins/serializers/carbon2/carbon2.go

  Lines 71 to 73 in 0c1e213

  	if _, ok := fieldValue.(string); ok {
  	continue
  	}

• telegraf/plugins/outputs/groundwork/groundwork.go

  Lines 285 to 288 in 0c1e213

  	case string, []byte:
  	g.Log.Warnf("string values are not supported, skipping field %s: %q", field.Key, field.Value)
  	continue
  	}

• telegraf/plugins/outputs/datadog/datadog.go

  Lines 213 to 214 in 0c1e213

  	case string:
  	return false

And probably many more..

[powersj]

I am a little concerned about the additional logging during field handling. This might reveal some new "issues" to end-users that are rather verbose. However, this handling is the correct change.

[powersj]

I've rebased on master to resolve the conflicts

[telegraf-tiger]

Download PR build artifacts for linux_amd64.tar.gz, darwin_amd64.tar.gz, and windows_amd64.zip.
Downloads for additional architectures and packages are available below.

⚠️ This pull request increases the Telegraf binary size by 1.08 % for linux amd64 (new size: 211.0 MB, nightly size 208.7 MB)

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Artifact URLs

DEB	RPM	TAR GZ	ZIP
amd64.deb	aarch64.rpm	darwin_amd64.tar.gz	windows_amd64.zip
arm64.deb	armel.rpm	darwin_arm64.tar.gz	windows_arm64.zip
armel.deb	armv6hl.rpm	freebsd_amd64.tar.gz	windows_i386.zip
armhf.deb	i386.rpm	freebsd_armv7.tar.gz
i386.deb	ppc64le.rpm	freebsd_i386.tar.gz
mips.deb	riscv64.rpm	linux_amd64.tar.gz
mipsel.deb	s390x.rpm	linux_arm64.tar.gz
ppc64el.deb	x86_64.rpm	linux_armel.tar.gz
riscv64.deb		linux_armhf.tar.gz
s390x.deb		linux_i386.tar.gz
		linux_mips.tar.gz
		linux_mipsel.tar.gz
		linux_ppc64le.tar.gz
		linux_riscv64.tar.gz
		linux_s390x.tar.gz