Adds an `Addrs` method to the Redis `authnFormat` interface so client addresses
can be delivered through the mounted secret rather than only the infrastructure
proto. `configFromProto` now calls `pf.Addrs` instead of reading
`cfg.GetAddrs()` directly. When the proto carries addresses they are used
as-is; otherwise `authenticatedFormat` reads the secret key named by the
projection's `addrs` field and parses a comma-separated `<host>:<port>` list,
trimming whitespace around each entry. `noSecretFormat` continues to return
only the proto addresses.  This supports provisioned endpoints whose address is
not known at config time and arrives via the secret alongside the credentials.

Extracts a `config()` helper for the shared nil-infra / nil-Redis checks used
by both `AuthConfig` and `Addrs`, plus a `resolveSecret` helper that resolves
an arbitrary projection field through the secret provider.

Bumps `fairway` to v1.30.0 for the `addrs` projection field.

Adds table tests for both formats covering proto passthrough, single and
comma-separated secret values, whitespace trimming, and the missing provider,
missing projection field, and key-not-found error paths.

Issue: gitlab-com/gl-infra/platform/runway/team#931

Previously, splitting the secret value on commas kept empty entries, so a value
with stray, doubled, or trailing commas yielded empty address strings that were
passed to the Redis client as invalid addresses.  Empty entries are now dropped
after trimming, and a value that resolves to no addresses returns the new
`ErrEmptyAddresses` sentinel with the raw value included for debugging.

Adds tests for stripping interleaved empty entries and for the
all-empty value returning an error.

Issue: gitlab-com/gl-infra/platform/runway/team#931

feat(redis): Resolve client addresses from the secret projection.

See merge request !551

Merged-by: Luke Hollinda <lhollinda@gitlab.com>
Approved-by: Matthew J. Hoad <mhoad@gitlab.com>
Approved-by: Luke Hollinda <lhollinda@gitlab.com>
Reviewed-by: GitLab Duo <gitlab-duo@gitlab.com>
Co-authored-by: Florian Forster <fforster@gitlab.com>