[jdk17u-dev] RFR: 8317374: Add Let's Encrypt ISRG Root X2

[Goetz Lindenmaier]

I backport this for parity with 17.0.10-oracle.

I had to adapt the location of the cert and checksum in the test.

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Commit messages:
 - Backport e6f46a43268808d0cbbb3bb93c73aa8e4cbfad83

Changes: https://git.openjdk.org/jdk17u-dev/pull/1950/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1950&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317374
  Stats: 39 lines in 3 files changed: 35 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/1950.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/1950/head:pull/1950

PR: https://git.openjdk.org/jdk17u-dev/pull/1950