[Security] Repository is vulnerable to MavenGate

[Nek-12]

https://blog.oversecured.com/Introducing-MavenGate-a-supply-chain-attack-method-for-Java-and-Android-applications/

Gradle task

./gradlew --write-verification-metadata pgp,sha256 --export-keys

 <component group="com.github.Commit451.coil-transformations" name="transformations" version="2.0.2">
         <artifact name="transformations-2.0.2.aar">
            <sha256 value="adbec226ce2c3a78b5e242e960971649b502cf3274aae421c48edd6bb94c7f56" origin="Generated by Gradle" reason="Artifact is not signed"/>
         </artifact>
         <artifact name="transformations-2.0.2.module">
            <sha256 value="58392a2a62b37ea8289a4633f9e4566c84ba5637806e6abbba87f14fac081aa4" origin="Generated by Gradle" reason="Artifact is not signed"/>
         </artifact>
      </component>

did not find a pgp public key in a remote repository or the artifact is not signed.
A fix is to:

1. Start signing all artifacts, if not signed yet
2. Upload a public pgp key used for signing artifacts to multiple public pgp repositories: https://keys.openpgp.org | https://pgp.mit.edu | https://keyserver.ubuntu.com/