feat: add --idp-configuration-id flag for multi-IDP Tableau Cloud sites

[jacalata]

Closes #393.

Summary

Tableau Cloud 2024.3+ supports up to 20 identity providers per site, and the REST API takes an idpConfigurationId attribute when creating users. Neither createsiteusers nor createUsers previously exposed the field, so operators on multi-IDP sites had to bypass tabcmd and script the REST API directly.

Adds --idp-configuration-id UUID to both createsiteusers and createUsers. The flag applies to every user in the batch. Argparse's add_mutually_exclusive_group enforces that --auth-type and --idp-configuration-id cannot both be passed, matching the REST API's own constraint (TSC's create_req raises if both attributes are set).

Scope decisions

• CSV format unchanged. The existing 8-column CSV is a shared cross-tool convention (Server web-UI user-import, tabcmd 1, tabcmd 2). Adding a 9th column here alone would create format divergence; that's better handled as a coordinated cross-tool update if per-user IDP assignment turns out to be needed.
• Batch-level assignment only in this PR. Real multi-IDP customers typically assign a batch of users to one IDP per run; a per-user 9th column can follow if there's demand.
• Refactor: the per-user --role / --auth-type / --idp-configuration-id application was duplicated between the two commands. Lifted into UserCommand.apply_cli_overrides so the branch is defined and tested in one place.

Test plan

• pytest tests/ — 347 passed, 2 skipped, 0 failed
• 6 new tests:
  • Parser: valid parse + mutual exclusion, on each of createsiteusers and createUsers (4 tests)
  • apply_cli_overrides: IDP flag clears a pre-existing auth_setting (covers the CSV col 8 + --idp-configuration-id interaction); role flag applied (2 tests)
• check-strings — SUCCESS, all i18n keys defined
• black --check — clean (using pinned black>=22,<23)
• mypy tabcmd/commands/user/ — 0 new errors
• tabcmd createsiteusers --auth-type SAML --idp-configuration-id x users.csv → argparse rejects with "not allowed with argument --auth-type" (confirmed at CLI)

Follow-ups (not in this PR)

• Per-user IDP assignment via a 9th CSV column would need to land coordinated with tabcmd 1 and the Server web-UI import to avoid format divergence.
• Docs on help.tableau.com should mention the new flag alongside the existing --auth-type doc for createsiteusers / createUsers.

🤖 Generated with Claude Code

[github-actions]

Coverage Report

File	Stmts	Miss	Cover	Missing
tabcmd
__main__.py	12	12	12	0%
_version.py	11	11	11	0%
tabcmd.py	15	15	15	0%
version.py	9	5	5	44%
tabcmd/commands
commands.py	10	10	10	0%
constants.py	77	24	24	69%
server.py	135	18	18	87%
tabcmd/commands/auth
session.py	394	50	50	87%
tabcmd/commands/datasources_and_workbooks
datasources_and_workbooks_command.py	157	18	18	89%
datasources_workbooks_views_url_parser.py	142	5	5	96%
delete_command.py	60	16	16	73%
export_command.py	120	25	25	79%
get_url_command.py	127	47	47	63%
publish_command.py	123	28	28	77%
runschedule_command.py	21	7	7	67%
tabcmd/commands/extracts
create_extracts_command.py	42	8	8	81%
decrypt_extracts_command.py	27	2	2	93%
delete_extracts_command.py	37	6	6	84%
encrypt_extracts_command.py	27	2	2	93%
extracts.py	20	2	2	90%
reencrypt_extracts_command.py	27	2	2	93%
refresh_extracts_command.py	48	10	10	79%
tabcmd/commands/group
create_group_command.py	29	5	5	83%
delete_group_command.py	27	2	2	93%
tabcmd/commands/project
create_project_command.py	46	8	8	83%
delete_project_command.py	35	4	4	89%
publish_samples_command.py	30	4	4	87%
tabcmd/commands/site
create_site_command.py	34	5	5	85%
delete_site_command.py	27	2	2	93%
edit_site_command.py	38	2	2	95%
list_command.py	77	12	12	84%
list_sites_command.py	29	2	2	93%
tabcmd/commands/user
add_users_command.py	29	5	5	83%
create_site_users.py	55	11	11	80%
create_users_command.py	55	10	10	82%
delete_site_users_command.py	43	5	5	88%
user_data.py	233	31	31	87%
tabcmd/execution
_version.py	2	2	2	0%
global_options.py	125	8	8	94%
localize.py	66	11	11	83%
logger_config.py	60	6	6	90%
tabcmd_controller.py	42	7	7	83%
TOTAL	2877	465	84%