Extended /certificates endpoint with additional SSL certs info

[willyborankin]

Description

Enhanced the /certificates endpoint to provide more detailed information. The endpoint now lists all certificates used by each node, with additional properties for each certificate, including:

• format
• alias
• serial_number
• has_private_key

Check List

• New functionality includes testing
• New functionality has been documented
• New Roles/Permissions have a corresponding security dashboards plugin PR
• API changes companion pull request created
• Commits are signed per the DCO using --signoff

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[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 7 lines in your changes missing coverage. Please review.

Project coverage is 71.49%. Comparing base (4aa7b1c) to head (a9d34d4).

Files with missing lines	Patch %	Lines
...lic/rest/api/ssl/CertificatesInfoNodesRequest.java	50.00%	3 Missing and 1 partial ⚠️
.../security/dlic/rest/api/CertificatesApiAction.java	66.66%	1 Missing and 1 partial ⚠️
...rg/opensearch/security/ssl/config/Certificate.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4882      +/-   ##
==========================================
+ Coverage   71.41%   71.49%   +0.07%     
==========================================
  Files         334      333       -1     
  Lines       22515    22533      +18     
  Branches     3585     3580       -5     
==========================================
+ Hits        16080    16110      +30     
+ Misses       4643     4632      -11     
+ Partials     1792     1791       -1     

Files with missing lines	Coverage Δ
...ch/security/dlic/rest/api/ssl/CertificateInfo.java	82.69% <100.00%> (+28.69%)	⬆️
...h/security/dlic/rest/api/ssl/CertificatesInfo.java	100.00% <100.00%> (ø)
.../api/ssl/TransportCertificatesInfoNodesAction.java	96.29% <100.00%> (+6.55%)	⬆️
...org/opensearch/security/ssl/SslContextHandler.java	98.86% <100.00%> (+0.02%)	⬆️
...a/org/opensearch/security/ssl/config/CertType.java	100.00% <100.00%> (ø)
...rg/opensearch/security/ssl/config/Certificate.java	61.64% <0.00%> (+3.31%)	⬆️
.../security/dlic/rest/api/CertificatesApiAction.java	80.00% <66.66%> (-3.79%)	⬇️
...lic/rest/api/ssl/CertificatesInfoNodesRequest.java	73.68% <50.00%> (-19.18%)	⬇️

... and 4 files with indirect coverage changes