feat: make utf-8 eci prefix configurable

[weiting-sflx]

Motivation

Some barcode scanners won't be able to read QR code that is prepended with UTF-8 ECI block, so we want to make the prefix configurable in the library that we utilize in our project endroid/qr-code-bundle

Changes

• Add a new parameter to the Encoder::encode function
• Adjust the Dockerfile

While building the docker image, we ran into errors and some depenencies were missing. After the modification, we were able to build the image and conducted the tests.