Explicitly disable CGO when building binary

[house-lee]

What happened:
After we upgraded to go 1.21 (from go 1.16) to build the droplet-agent, the binary started to crash on some of the droplets with error message /lib/x86_64-linux-gnu/libc.so.6: version GLIBC_2.32' not found`. (a report can be found here:#103)

Root cause:

• Starting in Go 1.20, c tool chain is no longer statically linked to the go binary. Go binaries now need to manually have the C libraries properly linked.
• Although we are not directly using CGO in this codebase, some standard libraries (net, os/user etc) that we use may have the cgo implementation chosen when building the binary, if the building environment has C tool chains available.
• While cgo is disabled by default starting from Go 1.20, it may still be enabled if the building environment has C tool chain available, unless explicitly disabled by setting the CGO_ENABLED flag

Related Links:

• /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.32' not found golang/go#58550
• https://go.dev/doc/go1.20#cgo

Thanks @iosonogio for reporting this

[house-lee]

Fix verified. Force merging due to emergency