Remove the release notes length limit

[loic-sharma]

Kudos to @dncnkrs for the original implementation in https://github.com/loic-sharma/BaGet/pull/610.

Allow BaGet to index packages with large release notes. For example: https://www.nuget.org/packages/chocolatey/0.10.6.1

• Test migration on new database:

  • [x] MySQL
  • [x] PostgreSQL
  • [x] SQL Server
  • [x] SQLite

• Test migration on existing database:

  • [x] MySQL
  • [x] PostgreSQL
  • [x] SQL Server
  • [x] SQLite

• Test indexing package with long release notes:

  • [x] MySQL
  • [x] PostgreSQL
  • [x] SQL Server
  • [x] SQLite

Addresses https://github.com/loic-sharma/BaGet/issues/609