Find dbadbmissingindexAdd Find-DbaDbMissingIndex

[deepeshd87]

Type of Change

• New feature (non-breaking change, adds functionality)
• Unit test is included

Implements #10770.

Purpose

dbatools has Find-DbaDbDuplicateIndex, Find-DbaDbUnusedIndex, and
Find-DbaDbDisabledIndex, but no missing-index counterpart. This adds a read-only
Find-DbaDbMissingIndex that surfaces suggestions from the sys.dm_db_missing_index_*
DMVs, ranked by impact, with a generated CREATE INDEX statement for review.

Approach (per the design discussed in #10770)

• Score uses avg_total_user_cost * avg_user_impact * (user_seeks + user_scans); the
  three inputs are returned as their own properties so results can be re-ranked.
• Per-database with WHERE mid.database_id = DB_ID(), correct on Azure SQL Database.
• On SQL 2019+, joins sys.dm_db_missing_index_group_stats_query alongside group_stats
  (not replacing it) for QueryHash / LastSqlHandle.
• Overlapping existing indexes are named in OverlappingIndex rather than filtered out.
• Returns instance StartTime and LastUserSeek/LastUserScan; warns at the 600-group
  collection limit; help notes the counter reset conditions.
• CREATE statement orders equality -> inequality -> INCLUDE, no edition-specific options.
• SQL 2005+ floor. Help notes VIEW SERVER STATE / VIEW SERVER PERFORMANCE STATE (2022+)
  requirement, that suggestions are candidates for human review, and links
  Invoke-DbaDiagnosticQuery.

Testing

Verified against a seeded fixture on SQL Server 2022: the DMV query, per-database
scoping, the ImpactScore and its inputs, the generated CREATE statement, the SMO
overlap detection, and the 2019+ query-text join (QueryHash/LastSqlHandle, no
double-counting) all return correctly. I wasn't able to run the full in-module Pester
suite locally, so I'm relying on CI for the end-to-end run.

(Second contribution — previously added Find-DbaDbQueryStoreRegression in 2.9.0.)