buildah: support passing build args as Tekton parameter list

[msugakov]

Description

For building ACS containers, we need to pass the same parameter to multiple tasks, one of them is buildah.

While there is BUILD_ARGS_FILE parameter (added in #935), it requires us writing a file in a workspace which, well, requires creating a custom task which will be a pain to get rid of in order to conform with EC.

Here I introduce an additional parameter of Tekton's type list - BUILD_ARGS_LIST.

Notes on testing

I developed it in a toy task and also verified how it runs in a pipeline: stackrox/scanner#1512. (Example runs, if you have access to the ACS tenant.)

A thing I'm concerned about is that now --build-arg-file option will point to a file that's outside of buildah Context directory (/build-args/build-args-unified). I think it should be fine but I was not able to test whether buildah will object (the latest version I get on my machine is 1.28 and it does not have that command-line option).

More broadly, I don't know how to test this change on real pipelines before it's merged so I'll appreciate some guidance. Also, leaving the template text 👇 as a reminder.

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[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

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[chmeliik]

@msugakov could you check #1023? Do you see some advantages in your approach over it?

[msugakov]

Closing in favor of #1023