RFR: 8318759: Add four DigiCert root certificates

[Rajan Halade]

This PR is to add 4 new TLS root certificates from Digicert, Inc. This CA has gone through https://www.oracle.com/java/technologies/javase/carootcertsprogram.html process.


The release-note is at [JDK-8319243](https://bugs.openjdk.org/browse/JDK-8319243)

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Commit messages:
 - 8318759: Add four DigiCert root certificates

Changes: https://git.openjdk.org/jdk/pull/16574/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16574&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318759
  Stats: 459 lines in 7 files changed: 456 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/16574.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16574/head:pull/16574

PR: https://git.openjdk.org/jdk/pull/16574