Mysql support [DO NOT MERGE]

[RichardAH]

[node_db]
type=mysql
online_delete=256
advisory_delete=0
path=ns

[relational_db]
backend=mysql

[mysql_settings]
user=root
pass=root
name=xahau
port=3306
host=localhost

[database_path]
/var/lib/xahaud/db

[debug_logfile]
/var/log/xahaud/debug.log

High Level Overview of Change

Context of Change

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (non-breaking change that only restructures code)
• Tests (you added tests for code that already exists, or your new feature included in this PR)
• Documentation update
• Chore (no impact to binary, e.g. .gitignore, formatting, dropping support for older tooling)
• Release

API Impact

• Public API: New feature (new methods and/or new fields)
• Public API: Breaking change (in general, breaking changes should only impact the next api_version)
• libxrpl change (any change that may affect libxrpl or dependents of libxrpl)
• Peer protocol change (must be backward compatible or bump the peer protocol version)