[telegraf] optional alternative config templates

[alespour]

This PR adds alternative config templates for aggregators, processors, inputs and outputs.

There have been a few issues so far where existing templates fail to render valid configuration elements (#433, #429, #375, #119, #111 etc). Existing templates are written with nesting that attempts to match generated output (especially for inputs), but it is insufficient and becomes difficult to maintain.

The new set of templates use one common recursive template that handles nesting without limits. The feature can be activated by setting tplVersion to 2 (either via --set helm option or as an entry in values file).

Config examples from the above mentioned issues are all together in charts/telegraf/ci/complex-values.yaml file and have been tested. The resulting telegraf.conf is valid and Telegraf runs with it.

Hopefully the new templates will support greater variety of yaml configs than existing templates. It may reduce the need to have an option to specify raw config (#358). But why not have both.

--

There is also a small amendment to workflow in this PR: after charts are tested (with success), logs are checked for messages that represent severe errors. In case of telegraf chart, when config file is invalid and Telegraf actually fails to start, ct install check result is success nevertheless.