feat(storage): support DynamoDB tablenamePrefix for cache driver

[AkashKumar7902]

What type of PR is this?

feature

Which issue does this PR fix: #2966

What does this PR do / Why do we need it:

Adds a new tablenamePrefix option to the dynamodb cache driver so administrators can configure all DynamoDB table names with a single prefix instead of declaring each table individually.

When tablenamePrefix is set, zot derives the following table names automatically:

Purpose	Derived name (with "tablenamePrefix": "Zot")
Dedupe blob cache	ZotBlobTable
Repo metadata	ZotRepoMetadataTable
Repo blobs info	ZotRepoBlobsInfoTable
Image metadata	ZotImageMetaTable
User data	ZotUserDataTable
API key	ZotApiKeyDataTable
Schema version	ZotVersionTable

Explicit per-table options (cacheTablename, repoMetaTablename, etc.) continue to take precedence, so existing configurations keep working unchanged.

Example new config:

"cacheDriver": {
    "name": "dynamodb",
    "endpoint": "http://localhost:4566",
    "region": "us-east-2",
    "tablenamePrefix": "Zot"
}

If an issue # is not available please add repro steps and logs showing the issue:

N/A — issue #2966 is open with the feature request.

Testing done on this change:

• Added unit tests in pkg/storage/cache_internal_test.go covering: derivation from prefix, explicit name precedence, missing/empty/non-string prefix, and missing/empty/non-string explicit table name.
• Added unit tests in pkg/meta/meta_internal_test.go covering the equivalent cases for the metadata tables.
• go test ./pkg/storage/ ./pkg/meta/ passes.
• golangci-lint run ./pkg/storage/... ./pkg/meta/... reports 0 issues.
• examples/config-dynamodb.json was simplified to use the new tablenamePrefix and validated via the unit tests.

Automation added to e2e:

No new e2e cases. The existing search/auth e2e suite still exercises explicit per-table configuration, which the new code path preserves verbatim.

Will this break upgrades or downgrades?

No. Existing configurations that use explicit table names continue to work because explicit names always take precedence over the derived prefix. Older zot versions ignore the new tablenamePrefix field.

Does this PR introduce any user-facing change?:

Yes — administrators can configure DynamoDB tables via a single tablenamePrefix instead of seven individual table-name fields.

DynamoDB cache driver now supports a `tablenamePrefix` option that derives all required table names (`<prefix>BlobTable`, `<prefix>RepoMetadataTable`, `<prefix>RepoBlobsInfoTable`, `<prefix>ImageMetaTable`, `<prefix>UserDataTable`, `<prefix>ApiKeyDataTable`, `<prefix>VersionTable`) from a single prefix. Explicit per-table options still take precedence.

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

[rchincha]

I like this change for better ux but concern is whether this is a breaking change.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.49%. Comparing base (993a17f) to head (4c1290e).
⚠️ Report is 33 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4016      +/-   ##
==========================================
+ Coverage   91.47%   91.49%   +0.02%     
==========================================
  Files         197      197              
  Lines       28353    28413      +60     
==========================================
+ Hits        25935    25997      +62     
+ Misses       1565     1563       -2     
  Partials      853      853              

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[rchincha]

I wouldn't drop support for earlier config. I would add this new behavior as an addendum. It is always useful to have the older way to override defaults.

[rchincha]

Restore this before the new entries. Will make the patch a lot cleaner.