Allow customize sbt opts

[lenguyenthanh]

This probably unnecessary, but sbt always crash on my machine with the current .sbtopts. I have to increase max memory to 16G (can be less but 6G is not enough).

[Baccata]

Mmm, I'm not against adding .sbtopts to .gitignore and removing the existing file, but I'd rather we used top-level environment variables in the ci-workflow than having a step copying the sbtopts file.

[kubukoz]

I don't have a strong opinion, but personally I've been passing -J-Xmx16g explicitly for my local usage.

[lenguyenthanh]

added

env:
  SBT_MAX_HEAP_SIZE: 6G # Max heap size for sbt

and use it every where

[Baccata]

@lenguyenthanh sorry for the churn, but I actually meant using the SBT_OPTS environment variable, to avoid repeating the change in many steps. See here : https://www.scala-sbt.org/1.x/docs/Command-Line-Reference.html#sbt+JVM+options+and+system+properties

[lenguyenthanh]

no problem, I'll update it, when I can reach my computer.

[lenguyenthanh]

added SBT_OPTS env variables with the same values as .sbtopts.example.

[Baccata]

Thank you !