Add JSON config examples to store.rs

[blakehatch]

Description

Please include a summary of the changes and the related issue. Please also
include relevant motivation and context
#958

Type of change

• This change requires a documentation update

Checklist

• Updated documentation if needed
• PR is contained in a single commit, using git amend see some docs

---

This change is 

[CLAassistant]

All committers have signed the CLA.

[adam-singer]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: 1 of 1 LGTMs obtained, and pending CI: Bazel Dev / ubuntu-22.04, Cargo Dev / macos-13, Cargo Dev / ubuntu-22.04, Installation / macos-13, Installation / macos-14, Installation / ubuntu-22.04, Publish image, Publish nativelink-worker-lre-cc, Remote / large-ubuntu-22.04, asan / ubuntu-22.04, docker-compose-compiles-nativelink (20.04), docker-compose-compiles-nativelink (22.04), integration-tests (20.04), integration-tests (22.04), macos-13, pre-commit-checks, ubuntu-20.04 / stable, ubuntu-22.04, ubuntu-22.04 / stable, windows-2022 / stable

[allada]

Reviewed 2 of 2 files at r2, all commit messages.
Reviewable status: 2 of 1 LGTMs obtained, and 2 discussions need to be resolved

---

nativelink-config/examples/redis.json line 14 at r2 (raw file):

                    "redis://127.0.0.1:6383/",   // Master node 3
                    "redis://127.0.0.1:6384/"   // Master node 3
                    //"redis://172.18.0.2:6379/"  // Master node 3

nit: Remove unused lines.

---

nativelink-config/src/stores.rs line 115 at r2 (raw file):

    ///     "backend": {
    ///       "filesystem": {
    ///         "content_path": "~/.cache/nativelink/content_path-ac",

nit: use /tmp/