fix(dockerfile): update dockerignore and base image

[vpavlin]

Description

When building docker image, the COPY command would also bring in nimcache/ and librln* which resulted in failures.

This does not happen in fresh repo clones, but after you run a build in the repo dir and attempt to build a container, it will fail

121.7 /rustc/5680fa18feaa87f3ff04063800aec256c3d4b4be/library/std/src/../../backtrace/src/symbolize/gimli/mmap_unix.rs:19:(.text._ZN3std12backtrace_rs9symbolize5gimli4mmap17h7e46d9a51e3a4761E+0x1a4): undefined reference to `mmap64'
122.2 collect2: error: ld returned 1 exit status
122.2 Error: execution of an external program failed: 'gcc  @networkmonitor_linkerArgs.txt'
122.3 stack trace: (most recent call last)
122.3 /app/vendor/nimbus-build-system/vendor/Nim/lib/system/nimscript.nim(429, 18)
122.3 /app/waku.nimble(71, 15) networkmonitorTask
122.3 /app/waku.nimble(35, 8)  buildBinary
122.3 /app/vendor/nimbus-build-system/vendor/Nim/lib/system/nimscript.nim(273, 7) exec
122.3 /app/vendor/nimbus-build-system/vendor/Nim/lib/system/nimscript.nim(273, 7) Error: unhandled exception: FAILED: nim c --out:build/networkmonitor  -d:chronicles_colors:none -d:insecure -d:postgres --verbosity:0 --hints:off -d:chronicles_log_level=TRACE -d:git_version="v0.22.0-rc.0-3-g2cb098" -d:release --passL:librln_v0.3.4.a --passL:-lm apps/networkmonitor/networkmonitor.nim [OSError]
122.3 make: *** [Makefile:206: networkmonitor] Error 1

Changes

• add nimcache and librln* to .dockerignore
• update the alpine base image

[Ivansete-status]

Wow! Super tricky issue! Thanks for it :)!

[SionoiS]

Thx! Detective @vpavlin