Follow-up cleanup of GitHub Actions migration (#116)

* Motivation:

Make use of more common GitHub Actions migration workflows and repository style changes.

Modifications:

* Unit tests workflows run redis in a separate services container to speed up unit tests
* Introduce `main.yml` which runs workflows on each commit to main and periodically to catch any regressions in merges or from upstream.
* Remove the docker files which are no longer used and contained outdated pipelines.
* Add Cxx interoperability checks

Result:

More in common with other GitHub Actions adoptions.

* disable strict concurrency

scripts/generate_contributors_list.sh

@@ -1,53 +0,0 @@
-#!/bin/bash
-##===----------------------------------------------------------------------===##
-##
-## This source file is part of the RediStack open source project
-##
-## Copyright (c) 2019 RediStack project authors
-## Licensed under Apache License v2.0
-##
-## See LICENSE.txt for license information
-## See CONTRIBUTORS.txt for the list of RediStack project authors
-##
-## SPDX-License-Identifier: Apache-2.0
-##
-##===----------------------------------------------------------------------===##
-##===----------------------------------------------------------------------===##
-##
-## This source file is part of the SwiftNIO open source project
-##
-## Copyright (c) 2017-2019 Apple Inc. and the SwiftNIO project authors
-## Licensed under Apache License v2.0
-##
-## See LICENSE.txt for license information
-## See CONTRIBUTORS.txt for the list of SwiftNIO project authors
-##
-## SPDX-License-Identifier: Apache-2.0
-##
-##===----------------------------------------------------------------------===##
-
-set -eu
-here="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
-contributors=$( cd "$here"/.. && git shortlog -es | cut -f2 | sed 's/^/- /' )
-
-cat > "$here/../CONTRIBUTORS.txt" <<- EOF
-	For the purpose of tracking copyright, this is the list of individuals and
-	organizations who have contributed source code to RediStack.
-
-	For employees of an organization/company where the copyright of work done
-	by employees of that company is held by the company itself, only the company
-	needs to be listed here.
-
-	## COPYRIGHT HOLDERS
-
-	- Apple Inc. (all contributors with '@apple.com')
-	- Globant Inc. (all contributors with '@globant.com')
-
-	### Contributors
-
-	$contributors
-
-	**Updating this list**
-
-	Please do not edit this file manually. It is generated using \`./scripts/generate_contributors_list.sh\`. If a name is misspelled or appearing multiple times: add an entry in \`./.mailmap\`
-EOF