[ADD] Support of DROP VIEW statements

[ovcharenko]

Fixing the exception like

sqllineage.exceptions.UnsupportedStatementException: SQLLineage doesn't support analyzing statement type [drop_view_statement] for SQL:DROP VIEW IF EXISTS view1

[codecov]

Codecov Report

Merging #456 (261edfa) into master (db24054) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #456   +/-   ##
=======================================
  Coverage   99.54%   99.54%           
=======================================
  Files          38       38           
  Lines        1986     1986           
=======================================
  Hits         1977     1977           
  Misses          9        9           

Files	Coverage Δ
sqllineage/core/parser/sqlfluff/extractors/drop.py	100.00% <100.00%> (ø)

[reata]

LGTM