Enclave build improvement ideas

[roshanrags]

Enclave building is a bit monolithic today which means intermediate steps can't effectively be cached. A clean rebuild using the Docker pipeline takes ~1.5 min.

There are three main culprits:

1. app
2. setup.sh and supervisord.conf
3. buildEnv (probably biggest)

Some improvement ideas

• Use /bin directly for binaries instead of /app. This means the binaries don't have to be copied to /app and can directly be used as inputs to buildEnv without needing to go in app.
• Break up setup.sh and supervisord.conf so each binary can define its own part which can be cached
• Break up buildEnv into multiple logical groupings which eventually combine into one. Each part can now be made into a derivation and cached separately.