Migrated PostgreSQL dialect implementation to its own repository.

Summary

Please we aware you can not create PostgreSQL Virtual Schemas using this JAR anymore.
PostgreSQL dialect implementation has been migrated to https://github.com/exasol/postgresql-virtual-schema.

We also enabled JOIN capabilities in MySQL dialect adapter, and started a FAQ documentation page.

Features

• #433: Enabled JOIN capabilities in MySQL dialect adapter.

Bug Fixes

• #427: Excluded transitive org.apache.httpcomponents:httpclient dependency to avoid CVE-2020-13956.

Documentation

• #408: Removed PostgreSQL dialect documentation as it has been migrated to https://github.com/exasol/postgresql-virtual-schema.
• #413: Improved documentation on ORACLE_CAST_NUMBER_TO_DECIMAL_WITH_PRECISION_AND_SCALE
• #402: Updated the documentation about implementing a new dialect.
• #426: Started FAQ documentation for Virtual Schemas.

Refactoring

• #408: Removed PostgreSQL dialect implementation as it has been migrated to https://github.com/exasol/postgresql-virtual-schema.
• #422: Refactored OracleQueryRewriter for more clarity.
• #424: Removed PostgreSQL dialect leftovers.

Dependency updates

• Updated com.exasol:virtual-schema-common-jdbc:7.0.0 to 8.0.0
• Removed org.postgresql:postgresql:42.2.18
• Removed org.testcontainers:postgresql:1.15.0
• Removed org.apache.httpcomponents:httpclient