[Feature] Support customizing JVM memory options via JVM_OPTS environment variable

[zhuxt2015]

Purpose of the pull request

Previously, JVM memory options in auto.sh were hardcoded as -Xms512M -Xmx2048M -XX:PermSize=512M -XX:MaxPermSize=1024M, and the Dockerfile worked around this by using sed to replace
the values at image build time with container-aware settings (-XX:+UseContainerSupport).

This PR removes the sed hack and introduces a cleaner approach:

• auto.sh now reads JVM options from the JVM_OPTS environment variable, falling back to the original hardcoded defaults if not set.
• The Dockerfile declares JVM_OPTS as an ENV variable with container-aware defaults (-XX:+UseContainerSupport -XX:InitialRAMPercentage=70.0 -XX:MaxRAMPercentage=70.0).

Benefits:

• Users can override JVM memory settings at runtime without rebuilding the image:
  docker run -e JVM_OPTS="-Xms1g -Xmx4g" dinky:latest
• Non-container deployments retain the original default values when JVM_OPTS is not set.
• Eliminates the fragile sed substitution that could silently fail if the hardcoded string changed.

Brief change log

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