Fix missing docker builder failure

[JenniferBuehler]

Important

this goes on top of #587 so will include those changes. Therefore, it's still in draft.

Add the docker buildx create step to build_container.sh so that skill building on a fresh system (where that wasn't run) doesn't fail.

To reproduce, on a fresh system setup (from the phase_1 branch), try to build a skill, e.g.:

pixi run --manifest-path src/aic/pixi.toml bash src/aic/flowstate/scripts/build_aic_flowstate_skills.sh --skill_name tare_force_torque_sensor_skill

Then observe:

build_aic_flowstate_skills.sh fails with ERROR: no builder "container-builder" found, followed by a misleading cascade of errors (open ./images/…/.tar: no such file, pull access denied for aic_flowstate_skills, and more).

Reason: build_container.sh runs docker buildx build --builder=container-builder but neither it nor the docs create that builder (side note: intrinsic_sdk_build/build.py does create it).

After running docker buildx create --name container-builder --driver docker-container, it works.

This PR adds this step to the build_container.sh so it doesn't have to be run manually. With this branch pixi run --manifest-path src/aic/pixi.toml bash src/aic/flowstate/scripts/build_aic_flowstate_skills.sh --skill_name tare_force_torque_sensor_skill passes on a fresh setup. Also prevents the "misleading cascade of errors" by setting set -eo pipefail.