Automate releases with a GH Actions

[kwin]

In order to ease releases, we should use both

• a central NC account for OSSRH for deploying to Sonatype OSSRH Maven repository
• a central NC PGP Private key for signing artifacts
• a Slack incoming Webhook token (https://ncchat.slack.com/apps/A0F7XDUAZ-incoming-webhooks?tab=more_info) for https://github.com/marketplace/actions/slack-notify or https://github.com/slackapi/slack-github-action

The credentials/key/token should be provided as organization secrets.

A release workflow like https://github.com/adobe/aem-core-wcm-components/blob/master/.github/workflows/maven-release.yml (adobe/aem-core-wcm-components#1345) can then be used by anyone with write access to the repo to spin a new release.

[kwin]

Open questions:

1. Where to publish the PGP Public Key (to ease verification)
2. RSA Key length and expiration date for the PGP keypair? Compare with https://infra.apache.org/openpgp.html#generate-key
3. Which email address and name to use for the public key and OSSRH account (new account opensource@netcentric.biz)?