fix: onboarding libraries to Librarian / location mixin workarounds

[suztomo]

Summary

This PR onboards 14 gems to Librarian that previously contained .owlbot.rb workarounds for spurious Google::Cloud::Location links (gapic-generator-ruby#824).

See tracking issue: googleapis/librarian#7444

Background & Analysis

Historically, gapic-generator-ruby converted markdown references to Google::Cloud::Location into invalid YARD cross-reference links ({::Google::Cloud::Location::Location ...}), which failed doc builds because the class is in an external gem dependency (google-cloud-location).
These gems maintained .owlbot.rb scripts with content.gsub to work around the bug.

With the upstream generator bug fix in gapic-generator-ruby#1211 (included in gapic-generator-cloud >= 0.51.0), the generator no longer emits invalid YARD links for cross-package mixin objects. As a result, the .owlbot.rb workarounds are obsolete and all 14 libraries can be safely onboarded to Librarian.

Onboarded Gems (14)

• google-cloud-discovery_engine-v1
• google-cloud-edge_container-v1
• google-cloud-firestore-admin-v1
• google-cloud-kms-v1
• google-cloud-memcache-v1
• google-cloud-memcache-v1beta2
• google-cloud-netapp-v1
• google-cloud-oracle_database-v1
• google-cloud-scheduler-v1
• google-cloud-scheduler-v1beta1
• google-cloud-tasks-v2
• google-cloud-tasks-v2beta2
• google-cloud-tasks-v2beta3
• google-cloud-vmware_engine-v1

Diff Analysis

1. OwlBot Removal: Removed .OwlBot.yaml, .owlbot.rb, and .owlbot-manifest.json from all 14 gem directories.
2. File Permissions: Snippet script permissions corrected from 755 to 644.
3. Pruning Unreferenced proto_docs: Removed unreferenced proto_docs/google/type/expr.rb in google-cloud-kms-v1 and google-cloud-vmware_engine-v1.
4. Documentation URLs: Minor updates to README and gemspec documentation links.

Local Verification

Ran full CI suite across all 14 gems:

toys ci --test --rubocop --doctest --gems google-cloud-discovery_engine-v1,google-cloud-edge_container-v1,google-cloud-firestore-admin-v1,google-cloud-kms-v1,google-cloud-memcache-v1,google-cloud-memcache-v1beta2,google-cloud-netapp-v1,google-cloud-oracle_database-v1,google-cloud-scheduler-v1,google-cloud-scheduler-v1beta1,google-cloud-tasks-v2,google-cloud-tasks-v2beta2,google-cloud-tasks-v2beta3,google-cloud-vmware_engine-v1

Result: All tests passed, 0 failures, 0 errors, 0 rubocop offenses.