Use ubuntu/squid docker image

[b-deam]

ITs were failing for me in #1602, and troubleshooting led me here:

$ docker run --rm --name squid -d -v it/resources/squid//squidpasswords:/etc/squid/squidpasswords -v it/resources/squid//squid.conf:/etc/squid/squid.conf -p 3128:3128 datadog/squid
Unable to find image 'datadog/squid:latest' locally
docker: Error response from daemon: pull access denied for datadog/squid, repository does not exist or may require 'docker login': denied: requested access to the resource is denied.
See 'docker run --help'.

$ docker search squid
NAME                         DESCRIPTION                                     STARS     OFFICIAL   AUTOMATED
sameersbn/squid                                                              222                  [OK]
squidfunk/mkdocs-material    Documentation that simply works                 113                  [OK]
minimum2scp/squid            squid3 cache service container running on de…   66                   [OK]
ubuntu/squid                 Squid is a caching proxy for the Web. Long-t…   40
b4tman/squid                 Squid container based on Alpine Linux           17                   [OK]
squidex/squidex              Squidex Headless CMS                            13
lucacri/squid-ext-conf       Squid server on alpine, gathering configurat…   12
babim/squid                  Squid 4 on alpine linux. With or without auth   3                    [OK]
photoprism/mkdocs-material   Tracks stable major versions of squidfunk/mk…   2
cloudreach/squid-utm         Squid Proxy UTM                                 1
kasmweb/squid                A proxy intended to redirect users to a Kasm…   1
boynux/squid-exporter        Squid metrics exporter for Prometheus           1                    [OK]
squids/squids-exporter                                                       0
squids/mysql                                                                 0
squids/mycilium                                                              0
squids/mysqlleader                                                           0
squids/mycilium-amd64                                                        0
squidex/nginx-proxy                                                          0
squids/qfb-mysql-8.0                                                         0
squidex/caddy-proxy                                                          0
squidtoon99/apiserver-rs                                                     0
squids/qfb-backup-job                                                        0
squidex/squidex-identity     Squidex Identity Server                         0
squidcache/buildfarm         Images for the project's Jenkins build farm     0
squids/fluent-bit                                                            0

The datadog/squid image doesn't seem to exist anymore, but because it was cached locally for me ITs continued to work. This commit updates it to use the ubuntu/squid Docker Image

[b-deam]

Ugh..

17:12:53 _________________ test_build_es_and_plugin_with_docker[es-it] __________________
17:12:53 
17:12:53 cfg = 'es-it'
17:12:53 
17:12:53     @it.random_rally_config
17:12:53     def test_build_es_and_plugin_with_docker(cfg):
17:12:53 >       assert (
17:12:53             it.esrally(
17:12:53                 cfg,
17:12:53                 "build --source-build-method=docker --revision=latest --target-arch aarch64 --target-os linux "
17:12:53                 "--elasticsearch-plugins=analysis-icu --quiet",
17:12:53             )
17:12:53             == 0
17:12:53         )
17:12:53 E       AssertionError: assert 64 == 0
17:12:53 E        +  where 64 = <function esrally at 0x7f9dbdcb0ca0>('es-it', 'build --source-build-method=docker --revision=latest --target-arch aarch64 --target-os linux --elasticsearch-plugins=analysis-icu --quiet')
17:12:53 E        +    where <function esrally at 0x7f9dbdcb0ca0> = it.esrally

[b-deam]

@elasticmachine run
rally/it-python38

[pquentin]

Thanks! Looks good to me.