REST API tests refactoring (Part 2)

[willyborankin]

Description

Changes:

• Moved test SslCertsApiTest into SslCertsRestApiIntegrationTest
• Fixed tests framework certificates generation for nodes.

Tests with the Legacy prefix removed since
new tests use randomization for paths

Check List

• New functionality includes testing
• New functionality has been documented
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.05%. Comparing base (6d35a0a) to head (dda9054).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4252      +/-   ##
==========================================
- Coverage   66.12%   66.05%   -0.07%     
==========================================
  Files         302      302              
  Lines       21758    21758              
  Branches     3522     3522              
==========================================
- Hits        14387    14372      -15     
- Misses       5609     5618       +9     
- Partials     1762     1768       +6     

Files	Coverage Δ
...arch/security/ssl/OpenSearchSecuritySSLPlugin.java	86.30% <ø> (ø)

... and 6 files with indirect coverage changes

[peternied]

It would be helpful to me if you worked backwards from the documentation-website to show what is getting removed and replaced. This would help me answer the question is this cohesive across how we consider certs.

What do you think?

[willyborankin]

In order to do not introduce breaking changes. Added a new endpoint instead in this PR: #4299

[DarshitChanpura]

LGTM. Left a clarifying question in a comment.

[opensearch-trigger-bot]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 128

To backport manually, run these commands in your terminal:

# Navigate to the root of your repository
cd $(git rev-parse --show-toplevel)
# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/security/backport-2.x 2.x
# Navigate to the new working tree
pushd ../.worktrees/security/backport-2.x
# Create a new branch
git switch --create backport/backport-4252-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 f130915daa969643c3996e0500e2bdbf3499c674
# Push it to GitHub
git push --set-upstream origin backport/backport-4252-to-2.x
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/security/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-4252-to-2.x.