fix: search channel releases so release image ls --version finds releases efficiently

[xavpaice]

When running replicated release image ls --channel ... --version ..., the CLI was only fetching the first page of channel releases (default page size of 20) and then filtering client-side by semver. This caused versions beyond the first page to fail with no release found with version ... in channel, even though the release existed and was visible in the UI.

This change:

1. Uses the API's server-side versionLabel filter when a specific version is requested, so only matching releases are returned instead of paginating through the entire channel history.
2. Keeps the previous pagination path as a fallback for edge cases where the version label differs from the semver.
3. Keeps the broader fix to ListChannelReleases so it paginates through all pages (used by the fallback and by GetCurrentChannelRelease).
4. Adds tests covering pagination behavior and the new versionLabel filter.

Fixes the reported issue where 2.17.12 in itrs-analytics/unstable could not be found via the CLI but was visible via the API on page 1.