[pkg/ottl] Add a function for concatenating lists

[lopes-felipe]

Component(s)

pkg/ottl

Is your feature request related to a problem? Please describe.

OTTL has no way to concatenate two (or more) lists into a single one, requiring to do some not-so-great workarounds with concat() and split(), and others.

Describe the solution you'd like

Add a new OTTL function that receives two lists and returns a new one containing all the items from both.

Describe alternatives you've considered

split(concat([concat(a, ","), concat(b, ",")], ","), ",")

Additional context

Use case: dynamically define the list of labels to be provided for the keep_keys from two sources.

[github-actions]

Pinging code owners:

• pkg/ottl: @TylerHelmuth @kentquirk @bogdandrutu @evan-bradley

See Adding Labels via Comments if you do not have permissions to add labels yourself.

[TylerHelmuth]

This a duplicate of #32141. I am closing this issue in favor of the other. @lopes-felipe please ping me if you feel the feature you're requesting is different.