Improve CI build time

[chrisdoherty4]

The CI took in excess of 15m to run per commit. This was largely due to environment emulation used to build binaries and docker images for the supported platforms and serial execution of validation tools.

This change set does the following:

• Cross compile binaries using the Go toolchain native support.
• Perform multi platform builds using a matrix build that parallelizes the builds.
• Run go test as a dedicated test job.
• Cache Go dependencies using the setup-go v3 caching feature.
• Updates all actions to their latest versions to ensure we don't begin failing due to various deprecations.

These changes results in an average build time reduction of roughly 600% from 19.5m to 3m (we should really think about using this setup across Tinkerbell).

To provide a sane local developer workflow the make image recipe has been updated to always build Linux binaries so it can be packaged into the final image. This means the binaries are no longer built in a container. The make build recipe is customizable using familiar GOOS and GOARCH variables defaulting to whatever your local platform is.

We may consider improving this in the future to limit version skew but given the reliability of the Go toolchain and Go being the only real dependency it seems OK to use the host environment for now. If more developers begin contributing we may need to normalize environments.

Minor bits

• Removed the Drone CI related Makefile recipes.
• Changed mergify to only require the images job given that job can't run without its pre-req jobs (all other jobs).

Closes #135

[codecov]

Codecov Report

Merging #145 (9d420dc) into main (ae4d443) will decrease coverage by 3.50%.
The diff coverage is 100.00%.

❗ Current head 9d420dc differs from pull request most recent head 866aaa6. Consider uploading reports for the commit 866aaa6 to get more accurate results

@@            Coverage Diff             @@
##             main     #145      +/-   ##
==========================================
- Coverage   24.19%   20.68%   -3.51%     
==========================================
  Files           7        7              
  Lines         682      672      -10     
==========================================
- Hits          165      139      -26     
- Misses        494      514      +20     
+ Partials       23       19       -4     

Impacted Files	Coverage Δ
internal/http/server.go	72.97% <100.00%> (-1.50%)	⬇️
internal/http/handlers.go	42.85% <0.00%> (-12.25%)	⬇️

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[chrisdoherty4]

@Mergifyio queue

[mergify]

Sorry but this command cannot run when the configuration is updated