Add SQL Server diagnostics (DataDog#23621)

* Add SQL Server diagnostics

* Add SQL Server diagnostics changelog

* Address Codex review on SQL Server diagnostics

- skip server-level VIEW SERVER STATE probe on Azure SQL Database
  and validate via sys.dm_exec_sessions (VIEW DATABASE STATE)
- probe msdb.dbo.syssessions when agent_jobs is enabled and not on RDS

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* Explicitly check VIEW DATABASE STATE on Azure SQL Database

On Azure SQL Database, `sys.dm_exec_sessions` always returns the
caller's own session row, so probing it cannot detect a missing
`VIEW DATABASE STATE`. Validate the permission with
`HAS_PERMS_BY_NAME(DB_NAME(), 'DATABASE', 'VIEW DATABASE STATE')`
before the session probe.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* Eliminate reference cycle in SQL Server diagnose

Mirrors the postgres fix in DataDog#23647: register a module-level
``run_diagnostics`` via ``functools.partial`` so a fresh ``SqlserverDiagnose``
worker is built per invocation and disposed of when ``_run()`` returns. The
previous shape kept a ``SqlserverDiagnose`` instance alive whose bound
``_run`` was held by ``Diagnosis``, forming a check → diagnosis → bound
method → diagnose worker → check cycle.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* Use NULL securable in HAS_PERMS_BY_NAME for VIEW DATABASE STATE

Azure SQL Database names can contain a dot. Passing ``DB_NAME()`` as the
securable made ``HAS_PERMS_BY_NAME`` parse the name as a multipart
identifier, returning 0 even when ``VIEW DATABASE STATE`` was granted and
producing a false-negative diagnostic. Using NULL targets the current
database unambiguously.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* Skip baseline diagnostic probes under only_custom_queries

When only_custom_queries is set the check skips load_basic_metrics and
database_metrics, so the Datadog login does not need access to
sys.dm_os_performance_counters or the database_metrics-only msdb tables.
Guard those probes (and VIEW SERVER STATE / VIEW ANY DEFINITION) so they
only run when the corresponding metric path is active or DBM is enabled.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* Address SQL Server diagnose review feedback

* Improve SQL Server diagnose remediation

* Add SQL Server diagnostics for Azure perf state, ODBC driver, and per-db access

Adds three high-signal pre-flight probes inspired by recurring SDBM
escalations:

- VIEW DATABASE PERFORMANCE STATE on Azure SQL Database / Managed
  Instance, probed with sys.dm_io_virtual_file_stats (SDBM-1707, SDBM-1504).
- ODBC driver installed: compares the configured driver to pyodbc.drivers()
  before connecting (SDBM-1939).
- Per-database access under autodiscovery: enumerates online user databases,
  applies the autodiscovery include/exclude filters, and probes each with
  USE/SELECT TOP 1 1 (SDBM-2293, SDBM-2401).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* Add per-database VIEW DATABASE STATE diagnostic

The existing per-database access probe only verified that the Datadog
login could USE each autodiscovered database. A login can pass that
probe and still produce no per-database DBM data because the per-db
DMV reads (sys.dm_exec_sessions filtered by database_id,
sys.dm_db_index_usage_stats, sys.dm_db_file_space_usage, ...) require
VIEW DATABASE STATE on the database — the exact permission the
existing remediation already told users to grant but never checked.

Extends the per-database loop to call HAS_PERMS_BY_NAME for VIEW
DATABASE STATE on each accessible database and emits a new
missing-per-database-view-state diagnosis with failures listed by
database name. Skipped on Azure SQL Database (per_database_access is
also skipped there) and when no database was accessible (the access
probe already reports that case).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* format

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: joelmarcotte

sqlserver/changelog.d/23621.added

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+Add explicit diagnostics for SQL Server setup validation.