Add ELM migrations commands (#1481)

* Add ELM migrations commands

* Add migration create options

* Fix style checks

* Use org base for ELM migrations

* Adjust BuildWheel task for Windows paths

* Allow GitHub.com targets and fix help YAML

* Simplify migration resume flow

* Add migrations command reference

* Fix BuildWheel task on Windows

* Fix markdown lint spacing

* Fix markdown lint and flake8 indentation errors

* Add --include-inactive help example and unit test for list migrations

* Fix convert_date_string_to_iso8601 returning datetime instead of string for tz-aware inputs

* Apply dev feedback: remove URL validation, fix validate-only default, unify flag naming, generic skip-validation help

* Update ELM migrations TSG with current params, codedev.ms troubleshooting, output formats

* TSG: add complete command/param reference, list step, cutover cancel, all optional params

* TSG: restructure as end-to-end guide with setup, lifecycle, walkthrough, and scenarios

* TSG: add fresh-user onboarding, concrete examples, status interpretation table, shell note

* docs: update TSG to use ADO org URL instead of separate ELM service URL

* docs: update migrations.md to use ADO org URL instead of ELM service URL

* Fix statusRequested field handling in pause/resume and update help URLs

* Make --agent-pool optional; server assigns default pool

- Remove required check for --agent-pool in create_migration
- Conditionally include agentPoolName in payload only when provided
- Server auto-assigns EnterpriseLiveMigrationPool when omitted
- Update tests: replace required-agent-pool tests with optional behavior tests

* Update migration changes and tests

* Promote validate-only migrations via PUT state update

* Improve migrations CLI UX validations and guidance

* Expand ELM migration docs and TSG guidance

* Support skip-validation names and integer values

* Add project filter support for migrations list

* Fix flake8 W503 in migration state check

* Fix markdown lint spacing and list formatting

* Fix remaining markdown lint issues in migration docs

* Fix Run_Style_Check missing dependency on Build_Publish_Azure_CLI_Test_SDK

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Co-authored-by: Bhuvan Shah <bhuvanshah@microsoft.com>