Publish to Maven

We need to publish CDE to maven, which makes RocketChip and other repository being able to use this without compiling from source, I have added the publish CI infrastructure, beside this we still need to set environments below:
```
PGP_PASSPHRASE: ${{ secrets.PGP_PASSPHRASE }}
PGP_SECRET: ${{ secrets.PGP_SECRET }}
SONATYPE_PASSWORD: ${{ secrets.SONATYPE_PASSWORD }}
SONATYPE_USERNAME: ${{ secrets.SONATYPE_USERNAME }}
```
I can provide my GitHub PGP key for signing and publishing, beside this, `SONATYPE_USERNAME` and `SONATYPE_PASSWORD` should be provided too, asking @mgielda for help.

Inspect the existing publish CI infrastructure first, then identify where the four named environment secrets are configured. Confirm that the CDE artifact can be signed and published for RocketChip and other repositories without compiling from source. The issue names no file or test path, so maintainer guidance and access to the required credentials are needed.

Written by the indexing model from the issue text.