feat: support pinning oasdiff CLI version in release.sh

[reuvenharrison]

Summary

Adds an optional second argument to release.sh so that each action release can atomically pin the oasdiff CLI image version used by all four Dockerfiles.

./release.sh v0.0.38 v1.13.5

• Patches FROM tufin/oasdiff:<current> → FROM tufin/oasdiff:v1.13.5 in all four Dockerfiles (breaking/, changelog/, diff/, pr-comment/)
• Includes the Dockerfiles in the same commit as the README bump, with an updated commit message: chore: bump action to v0.0.38, pin oasdiff to v1.13.5
• Shows the current oasdiff version alongside the action version in the opening log line, so you can see at a glance what is changing
• Without the second argument the script behaves exactly as before (backwards compatible)

Motivation

Follows from the review of #89: pinning by version tag is the right direction, but only sustainable if bumping the version is automated rather than a manual edit across four files.

Test plan

• Dry-run: verify sed patterns replace the FROM line correctly for both :stable and a pinned tag
• Smoke-run against a test branch to confirm the commit includes the Dockerfiles when the argument is provided and excludes them when it is not

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