Switch to using abstract-cache

[jsumners]

This PR switches out the requirement for Catbox style caches with a requirement for abstract-cache style caches. This allows greater flexibility due to the fact that abstract-cache allows re-using established connections. So, for example, the user could register multiple instances of fastify-caching for different routes while using the same connection:

const redis = require('ioredis')({host: '127.0.0.1'})
const abcache = require('abstract-cache')({
  driver: {
    name: 'abstract-cache-redis',
    options: {client: redis}
  }
})

const fastify = require('fastify')()
const fastifyCaching = require('fastify-caching')

fastify.register((instance, opts, next) => {
  instance.register(fastifyCaching, {
    segment: 'foo',
    cache: abcache
  })

  instance.get('/foo', async function (req, reply) {
    await this.cache.set('foo', 'foo', 1000) // goes to the 'foo' Redis collection
    return {foo: 'foo'}
  })

  next()
})

fastify.register((instance, opts, next) => {
  instance.register(fastifyCaching, {
    segment: 'bar',
    cache: abcache
  })

  instance.get('/bar', async function (req, reply) {
    await this.cache.set('bar', 'bar', 1000) // goes to the 'bar' Redis collection
    return {bar: 'bar'}
  })

  next()
})

[delvedor]

LGTM

[allevo]

LGTM