Add support for PostgreSQL LISTEN/NOTIFY syntax

[wugeer]

This PR supports LISTEN/NOTIFY clause for postgres dialect,. For more information, please refer to:
https://www.postgresql.org/docs/current/sql-listen.html
https://www.postgresql.org/docs/current/sql-notify.html

It also introduces the following keywords:

• LISTEN
• NOTIFY

This resolves issue #1481

[iffyio]

LGTM! cc @alamb

[wugeer]

Sorry, I mixed up the documentation links for listen and notify in the last commit. And currently, only PostgreSQL supports listen and notify syntax, so I've added a dialect check and moved the tests to sqlparser_postgres.rs. Could you please review it again? @iffyio

[iffyio]

Thanks @wugeer just one comment around the naming otherwise I think this looks good!

[iffyio]

LGTM! cc @alamb

[alamb]

Thank you @wugeer and @iffyio

[coveralls]

Pull Request Test Coverage Report for Build 11685106929

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

• 68 of 78 (87.18%) changed or added relevant lines in 5 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.005%) to 89.391%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/dialect/mod.rs	2	4	50.0%
src/dialect/postgresql.rs	2	4	50.0%
tests/sqlparser_common.rs	43	49	87.76%

Totals
Change from base Build 11651598157:	-0.005%
Covered Lines:	30568
Relevant Lines:	34196

---

💛 - Coveralls

[iffyio]

Will look to merge this given we're pending only a ci run

[alamb]

Woohoo -- it is great to see you merging PRs @iffyio