Regression fix: Selects docker image target fpr local-build-all.sh

[Tradunsky]

Build config format has changes in this commit: e4c9827#diff-c08c571600c3c85d24ce5e2af55959c64188e70844c69e941a2ea91ecd7691e1
this commit adjusts local-build-all.sh script to the new config format.

Before:

After:

A side note: Seems like a docker image is missing from public docker hub (or private docker registry not specified) flb-amazonlinux/2.arm64v8:

ERROR: failed to solve: arm64v8/amazonlinux:2: failed to resolve source metadata for docker.io/arm64v8/amazonlinux:2: no match for platform in manifest: not found
+ echo 'Error building main docker image flb-amazonlinux/2.arm64v8'
Error building main docker image flb-amazonlinux/2.arm64v8
+ exit 1

---

Testing
Before we can approve your change; please submit the following in a comment:

• [N/A] Example configuration file for the change
• Debug log output from testing the change

• [N/A] Attached Valgrind output that shows no leaks or memory corruption was found

If this is a change to packaging of containers or native binaries then please confirm it works for all targets.

• Run local packaging test showing all targets (including any new ones) build.
• Set ok-package-test label to test for all targets (requires maintainer to do).

Documentation

• [N/A] Documentation required for this feature

Backporting

• [N/A] Backport to latest stable release.

---

Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.