docs: compatibility matrix for SS 12.0 + event-pipeline folder rename

[jagger]

Summary

Phase 4 of the v0.62.0 documentation refresh. Stacks on top of #451 — base will retarget to dev once that merges.

Compatibility matrix (docs/getting_started/compatibility.md):

• Intro now states the module is tested through Secret Server 12.0 (was vague "latest Secret Server release")
• Add an SS 12.0 notes subsection covering the response-filtering fixes shipped in v0.62.0 (Get-TssConfiguration, Get-TssRpcPasswordType, Get-TssDirectoryServiceSyncStatus, plus the general FilterTssResponse pass)
• The minimum-version function table is unchanged — v0.61.x/v0.62.0 introduced bug fixes against existing cmdlets, not new minimum-version-required cmdlets

Folder rename:

• docs/commands/event-pipeline/ → docs/commands/event-pipelines/
• docs/commands/event-pipeline-policy/ → docs/commands/event-pipeline-policies/
• Plural matches sibling folders (secrets/, folders/, reports/, etc.)
• Each moved page gets a redirect_from: frontmatter entry pointing at its old URL so existing inbound links don't 404
• Self-links inside each page's RELATED LINKS section updated to the new path
• Readme nav titles updated to plural ("Event Pipelines", "Event Pipeline Policies" — the latter was already plural)
• Added jekyll-redirect-from plugin to docs/_config.yml so the redirects actually render on GitHub Pages

Out of scope:

• The source folders src/functions/event-pipeline/ and src/functions/event-pipeline-policy/ are unchanged. Renaming source folders touches the build pipeline, tests, and .ps1 files — would be a separate change.
• The misplaced Add-TssEventPipeline.md / Remove-TssEventPipeline.md files that live under event-pipeline-policies/ (they belong under event-pipelines/) — moving them changes URLs again and is out of scope for this PR.

Test plan

• Render the Jekyll site locally (or via GitHub Pages preview) and confirm:
  • "Event Pipelines" and "Event Pipeline Policies" appear in the Commands nav at orders 20 and 21
  • Curl an old URL such as https://thycotic-ps.github.io/thycotic.secretserver/commands/event-pipeline/Get-TssEventPipeline.html and confirm it 301s to the new plural location
  • Compatibility page renders the new SS 12.0 notes subsection
• grep -rn "commands/event-pipeline/\|commands/event-pipeline-policy/" docs/ returns only redirect_from: lines, no real link remnants

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