Build Alloy for linux/riscv64

[macabu]

PR Description

Builds binaries and OCI images for linux/riscv64. I was able to validate that the binary worked and was sending metrics to Loki (sample config).

user@bananapif3:~/Projects/alloy/dist$ file alloy-linux-riscv64
alloy-linux-riscv64: ELF 64-bit LSB executable, UCB RISC-V, RVC, double-float ABI, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux-riscv64-lp64d.so.1, BuildID[sha1]=252737e53b37668ec9a2b5baad07bbe4ea82ef1f, for GNU/Linux 4.15.0, stripped

user@bananapif3:~/Projects/alloy/dist$ ldd alloy-linux-riscv64
	linux-vdso.so.1 (0x0000003f946d8000)
	libc.so.6 => /lib/riscv64-linux-gnu/libc.so.6 (0x0000003f94564000)
	/lib/ld-linux-riscv64-lp64d.so.1 (0x0000003f946da000)

Which issue(s) this PR fixes

Fixes #1036

Notes to the Reviewer

PR Checklist

• CHANGELOG.md updated

[CLAassistant]

All committers have signed the CLA.

[macabu]

I believe this should be regenerated by one of the maintainers? 🙈

[macabu]

Rabbit hole is deeper 😄 (closing for now)