feat: add slice tool to mcp

[yelizhenden-mdb]

Proposed changes

Jira ticket: CLOUDP-393141

This PR implements A new tool that creates a filtered subset of a loaded OpenAPI specification and saves it as a virtual spec for further use.

Input:

• sourceAlias (required) — alias of the spec to slice
• saveAs (required) — agent-chosen alias for the resulting virtual spec
• tags, operationIds, paths (at least one required) — filter criteria, combined with OR logic

Output: success message + the new alias

Key behaviours:

• Validates saveAs format (lowercase letters, numbers, hyphens) and uniqueness
• Delegates filtering to FOASCLI slice, which also cleans up unreferenced schemas, parameters, and responses
• The same source spec can be sliced multiple times under different aliases

Checklist

• I have signed the MongoDB CLA
• I have added tests that prove my fix is effective or that my feature works

Changes to Spectral

• I have read the README file for Spectral Updates

Further comments

[andmatei]

LGTM