feat(ADDON-87180): introduce dedicated index_name validator type

[okashaev-splunk]

Summary

• Replaces the two-validator combination (regex pattern + string length) for
  Splunk index name validation with a single dedicated index_name validator type
• Adds IndexNameValidator Zod schema registered in AllValidators and AnyOfValidators
• Adds IndexNameValidator in validator_builder.py that generates validator.IndexName()
• Updates IndexEntity.long_form() and migrateIndexTypeEntity() to emit {"type": "index_name"}
• Adds IndexNameValidator definition to schema.json and registers it in AnyValidator and SingleSelectEntity validators
• Updates expected REST handler fixtures to emit validator.IndexName()
• Updates test addon globalConfig.json to use index_name validator type
• Bumps splunktaucclib minimum version to 8.2.0 which ships validator.IndexName()

Note: No UI-side case 'index_name' is needed — backend validation on save is the intended contract for this flow.

Test plan

• Existing unit tests for IndexEntity updated and passing
• New validator_builder test case added with golden file validator_builder_result_index_name
• schema.json updated — Python schema validation accepts {"type": "index_name"}
• Expected REST handler fixtures updated to emit validator.IndexName()
• Test addon globalConfig.json updated to use index_name validator
• splunktaucclib minimum version bumped to 8.2.0

🤖 Generated with Claude Code

[wtobis-splunk]

Requesting changes. This introduces a new validator contract across backend generation, Python schema, frontend runtime validation, bundled UI assets, and splunktaucclib runtime support, but the PR only wires part of that surface. Several paths now either silently skip validation or generate handler code that the currently required runtime library does not provide.

[wtobis-splunk]

Blocking: the UI runtime validator does not handle index_name. ui/src/util/Validator.ts switches over validator types but has no case 'index_name', so after this migration the old regex/string checks are removed and invalid index names are silently accepted in the form. Please add runtime validation and tests for valid/invalid index values before replacing the old validators.

[okashaev-splunk]

No UI left intentionally, this means no validation will be done during field edit. However when user tries to save the form backend validation is triggered not letting to close from with save operation.
Keeping regexes in UI makes central validation endpoint useless UI validation will always come before backend

[wtobis-splunk]

Thanks, backend-only validation on save is acceptable for this flow. No need to add a frontend case 'index_name' or duplicate the index-name checks in the UI if this is the intended contract.

[wtobis-splunk]

This adds index_name as a schema-level validator type, but the docs still describe the old contract. docs/entity/components.md says the index field has two internal validators (regex + length), and docs/entity/validators.md does not document index_name even though it is now accepted by AnyValidator. Please update the docs so users know whether index_name is public and so the index component documentation matches the generated config.

[github-actions]

Code Coverage ⚠️

Type	PR	Develop	Change	Status
Line Coverage	94.35%	94.38%	0.04%	🔴 Decreased
Branch Coverage	90.66%	90.66%	0.00%	⚪ Unchanged