Add goreleaser, sboms, slsa3, sigstore and homebrew support

[rdimitrov]

The following PR covers the following changes.

Adds

• Introduces GoReleaser
• Builds and releases medic binaries for [linux, windows, darwin] and [amd64, arm64]
• Binaries are released as archived binaries (prev. plain binaries). For some reason setting the format to binaries made the SBOMs disappear from the released files.
• Generate SLSA3 provenance for each released version (keyless)
• Verify the SLSA3 provenance for each released version (Fixes an issue actually in the current action which only verifies one of the versions)
• Generate SBOMs for each released version using Syft
• Sign each released version using cosign (keyless)
• Publish a homebrew formula so we can install medic through brew install stacklok/tap/medic. (note: adding a formula to the homebrew-core tap is for post-MVP)

Removes

• Removed the existing slsa-go-releaser action which was used to build and release medic and also generate provenance

Unchanged

• Kept the same trigger conditions for the release process - on release created event

Blocking

• Create a PAT token for this action to push to https://github.com/stacklok/homebrew-tap
• Add that token as HOMEBREW_TAP_GITHUB_TOKEN environment variable to this repository
• For home-brew to work, we have to open source both the homebrew-tap and mediator repos. There's a way to add support for private repos but I thought it's not worth it since we are open sourcing soon anyway.
• SLSA provenance and cosign push to public transparency logs. We have to decide if this is a problem or not prior to open sourcing this. On that note, I realised that we are already doing that with the current action (@lukehinds).
• The setting private-repository: true is actually very misleading - https://github.com/stacklok/mediator/blob/2c9034069ed71519aa673e59b1ec77195f4cea51/.github/workflows/slsa-go-releaser.yml#L58 Reference - SLSA docs

Fixes: #1249
Fixes: #1250

[rdimitrov]

FYI - In case you want to see this in action, I've Implemented that first for another project as a proof-of-concept - https://github.com/rdimitrov/tuf-client-cli/actions/runs/6679372755