Add missing metadata for jackson-base pom 2.12.1

Problem: When merging #5824, the absence of this entry caused a build
failure at dependency verification time against JDK11 and JDK15 on
Ubuntu-latest [1]. It may also cause failures on other JDK/OS
combinations, but the GitHub workflow was aborted before those failures
couldhave occurred. In any case, this omission did not create build
failures on any of the local development machines that tested the
aforementioned PR. Reasons for this discrepancy are unknown.

Solution: manually fetch the pom from [2], run `sha256sum` on it locally
and commit the result to the verification metadata file.

[1]: https://github.com/bisq-network/bisq/runs/4249640611?check_suite_focus=true#step:6:33
[2]: https://repo1.maven.org/maven2/com/fasterxml/jackson/jackson-base/2.11.1/jackson-base-2.11.1.pom

gradle/verification-metadata.xml

@@ -85,6 +85,11 @@
             <sha256 value="af650fa4dd400bc5769320bcef08ed93813f349cabe8213d469acafbbd945d8a" origin="Generated by Gradle"/>
          </artifact>
       </component>
+      <component group="com.fasterxml.jackson" name="jackson-base" version="2.12.1">
+         <artifact name="jackson-base-2.12.5.pom">
+            <sha256 value="93a8c78755a31977508021dbb3883c0dd740a06bb1c67ff4942e096c132419f5" origin="Added by cbeams"/>
+         </artifact>
+      </component>
       <component group="com.fasterxml.jackson" name="jackson-base" version="2.12.5">
          <artifact name="jackson-base-2.12.5.pom">
             <sha256 value="82f7beac170a2e9c3867daf997a79c1fe984c0041be380d1b2935062412a2129" origin="Generated by Gradle"/>