Add support for TLS-backed connections to Redis

[iKenndac]

This PR adds TLS support to the current stable release of vapor/redis (and the underlying RediStack 1.x). There are three behaviour changes (all additive):

• The RedisConfiguration struct now has optional tlsConfiguration and tlsHostname properties.

• The RedisConfiguration struct constructors that take URLs now handle rediss URLs and will fill out the tlsConfiguration and tlsHostname properties with default values from the URL.

• If the tlsConfiguration and tlsHostname properties are set, a custom ClientBootstrap will be created when it's time to create a RedisConnectionPool, adding a NIOSSLClientHandler to the pipeline on top of the ones created by addBaseRedisHandlers(). If the properties aren't set, the behaviour is as before.

This PR allows vapor/redis to be used with hosting services like Heroku, which (in certain configurations) require that you connect to Redis using TLS.

Ramifications on Future Versions

The logic for this PR was "borrowed" from this PR on RediStack: https://gitlab.com/swift-server-community/RediStack/-/merge_requests/160

I'm aware that work is being done in RediStack to add this "properly". However, I need to use TLS now and I'd like to stay on stable releases as much as possible. I'm aware there's already work on the main branch here for RediStack 2.x. This PR is branched from the 4.6.0 release — hopefully it can be merged into a new 4.x release to tide us over until 5.x comes along.

Example Usage

Here's how I'm using this addition in my Vapor app running on Heroku. Heroku self-signs its TLS certificates, so I need to turn off certificate verification:

guard let redisUrl = Environment.get("REDIS_TLS_URL") else { throw Abort(.expectationFailed) }

let poolOptions = RedisConfiguration.PoolOptions(minimumConnectionCount: 1, connectionRetryTimeout: .seconds(10))

var tlsConfig: TLSConfiguration = .makeClientConfiguration()
tlsConfig.certificateVerification = .none

var redisConfig = try RedisConfiguration(url: redisUrl, pool: poolOptions)
redisConfig.tlsConfiguration = tlsConfig
app.redis.configuration = redisConfig

[gwynne]

@0xTim Looks like a straightforward and clean addition of support for 1.x, once the conflicts are resolved.

[iKenndac]

Whoops, I saw those 5.0.0 alpha releases and thought they were on main, so I branched from 4.6.0. My bad — fixed now!

[0xTim]

Released in https://github.com/vapor/redis/releases/tag/4.7.0

[iKenndac]

Thank you! :heart: