[cpesuggest] Add CPE prefix for third_party/jsoncpp/README.chromium.

To verify the correctness of the suggested CPE Prefix, please follow
the steps below:
1. Visit the National Vulnerability Database (NVD) page for the
   suggested CPE Prefix here:
   https://nvd.nist.gov/products/cpe/search/results?namingFormat=2.2&keyword=cpe:/a:jsoncpp_project:jsoncpp&status=FINAL%2CDEPRECATED
2. Check whether the third-party dependency for which the CPE Prefix is
   suggested matches the project listed in the NVD page.
3. If the open source project matches and the CPE prefix is not
   deprecated, please Code-Review+1 and submit if you have enough votes.
4. If the open source project does not match or if the CPE prefix is
   deprecated, please add the incorrect suggestion to
   go/ignored_cpes_textproto and add the reason why the suggestion is
   incorrect.

Adding CPE prefixes to a README.chromium file is recommended practice
[1] to enable automated vulnerability monitoring. For more
information on how CPE prefixes are used see the Chromium Third
Party docs [2].

[1] https://chromium.googlesource.com/chromium/src/+/HEAD/third_party/README.chromium.template

[2] https://chromium.googlesource.com/chromium/src/+/HEAD/docs/adding_to_third_party.md#add-a-readme_chromium

Bug: 290294330
Change-Id: If4662e15530574de7075b9d8488c530f8b29929f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7869095
Commit-Queue: Joey Scarr <jsca@google.com>
Reviewed-by: Rachael Newitt <renewitt@google.com>
Auto-Submit: CPE Updater <chops-security-cronjobs-cpesuggest@prod.google.com>
Reviewed-by: Joey Scarr <jsca@google.com>
Cr-Commit-Position: refs/heads/main@{#1634669}
NOKEYCHECK=True
GitOrigin-RevId: 6c3a4b6abe202d79b1e9ad14be2e4fb8369e6b8b