MS SQL Server: add support for IDENTITY column option

[7phs]

This PR implements support IDENTITY column option of T-SQL (MS SQL Server). Example:

CREATE TABLE [dbo].[table_name]
(
  [columnA] int IDENTITY(1,1) NOT NULL,
  [columnB] nvarchar(255) NULL
)

[coveralls]

Pull Request Test Coverage Report for Build 10959695994

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 86 of 90 (95.56%) changed or added relevant lines in 3 files are covered.
• 1215 unchanged lines in 9 files lost coverage.
• Overall coverage increased (+0.01%) to 89.349%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tests/sqlparser_mssql.rs	72	76	94.74%

Files with Coverage Reduction	New Missed Lines	%
tests/sqlparser_bigquery.rs	1	90.25%
src/dialect/duckdb.rs	1	61.11%
src/dialect/generic.rs	1	63.41%
src/dialect/postgresql.rs	2	68.48%
src/dialect/mod.rs	11	68.13%
tests/sqlparser_postgres.rs	52	88.61%
src/ast/mod.rs	289	82.43%
tests/sqlparser_common.rs	406	89.76%
src/parser/mod.rs	452	93.35%

Totals
Change from base Build 10892026190:	0.01%
Covered Lines:	29689
Relevant Lines:	33228

---

💛 - Coveralls

[iffyio]

LGTM! cc @alamb

[alamb]

Thanks @7phs and @iffyio