[release-1.23] Opa blog post

[istio-testing]

Manual cherrypick required.

#15134 failed to apply on top of branch "release-1.23":

Applying: add blog post
Applying: Add intro, adjust policy
Applying: Remove other titles and descriptions
Applying: Pass lint
Applying: sort alphabetically
Using index info to reconstruct a base tree...
M	.spelling
Falling back to patching base and 3-way merge...
Auto-merging .spelling
CONFLICT (content): Merge conflict in .spelling
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0005 sort alphabetically
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".