add standalone dbs and configs

[ceyonur]

This pull request introduces significant changes to the plugin/evm package to support standalone databases, update configurations, and enhance testing. The most important changes include adding new database-related configurations, updating the VM struct and initialization process, and modifying tests to accommodate the new skipStandaloneDB flag.

Database Configuration Enhancements:

• plugin/evm/config.go: Added new database-related configurations including UseStandaloneDatabase, DatabaseConfigContent, DatabaseConfigFile, DatabaseType, DatabasePath, and DatabaseReadOnly. Also added a new type PBool to handle optional boolean values. [1] [2] [3] [4]

VM Struct and Initialization Updates:

• plugin/evm/vm.go: Updated the VM struct to include a skipStandaloneDB flag and chainAlias. Modified the Initialize method to handle standalone database initialization and metrics setup. Added new methods useStandaloneDatabase, getDatabaseConfig, initializeDBs, and createDatabase to support the new database configurations. [1] [2] [3] [4] [5]

By default VM uses a standalone database if there is no accepted block in AvalancheGo's provided database. use-standalone-database is nil by default, and can override the default behavior by taking false/true as value.

Test Updates:

• plugin/evm/block_test.go, plugin/evm/syncervm_test.go, plugin/evm/tx_gossip_test.go, plugin/evm/vm_test.go: Updated various test cases to set the skipStandaloneDB flag to true to ensure tests run with the intended database configuration. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]

These changes enhance the flexibility and configurability of the EVM plugin, allowing for more robust database management and testing.

How this was tested

Tested with DFK

How is this documented

Need to document in docs repo.

Some metrics running the LevelDB in DFK testnet with two similar spec machines: