Cherry-pick of PR #19134 to 7.x branch. Original message:

What does this PR do?

When {{ .tags }} is evaluated in the module config it not written in the correct format.
This fixes that issue and also conditionally enables publisher_pipeline.disable_host
based on whether tags contains forwarded to be consistent with every other module
that allows for var.tags to be set (relates: #13920).

For example (https://play.golang.org/p/LUr-X94msd1):

var.tags: [foo, bar]

will be written into the config as

tags: [foo bar]

which is a single value array containing the string "foo bar" rather than two tags.

Why is it important?

If a user specified more than one tag in a module config then they would not have had the expect tags in their events.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Related issues

• Relates Setting host.* in Beats that forward data #13920