Review instances of determinate.systems for replacement or other action

[abathur]

We'll need to get these worked out before this can be fully official unofficial. They probably aren't all ripe yet, so we'll probably either need to do a few batches or hold off on this until the infra bits are in place?

Reference files/counts:

.github/PULL_REQUEST_TEMPLATE.md:3
.github/workflows/release-branches.yml:3
.github/workflows/release-prs.yml:3
.github/workflows/release-tags.yml:2
CONTRIBUTING.md:4
README.md:12
src/action/common/place_nix_configuration.rs:1
src/cli/subcommand/install.rs:1
src/cli/subcommand/uninstall.rs:2
src/planner/macos/mod.rs:2
src/planner/mod.rs:1
src/settings.rs:2
tests/fixtures/linux/linux.json:2
tests/fixtures/linux/steam-deck.json:2
tests/fixtures/macos/macos.json:2
upload_s3.sh:2

See also/previously:

• round up user-facing references to the detsys repo/domain #10

[abathur]

Some instances of this will center on documentation, which will be interesting :)

For example, detsys appear to have figured out how to detect and throw a better warning about system profiles that block volume mounting, in which case the installer links to https://determinate.systems/solutions/macos-internal-disk-policy/. (This is currently the only link into their domain's /solutions/ path, so maybe it's the only one.