* enable registering backend muxed plugins in plugin catalog
* set the sysview on the pluginconfig to allow enabling secrets/auth plugins
* store backend instances in map
* store single implementations in the instances map
cleanup instance map and ensure we don't deadlock
* fix system backend unit tests
move GetMultiplexIDFromContext to pluginutil package
fix pluginutil test
fix dbplugin ut
* return error(s) if we can't get the plugin client
update comments
* refactor/move GetMultiplexIDFromContext test
* add changelog
* remove unnecessary field on pluginClient
* add unit tests to PluginCatalog for secrets/auth plugins
* fix comment
* return pluginClient from TestRunTestPlugin
* add multiplexed backend test
* honor metadatamode value in newbackend pluginconfig
* check that connection exists on cleanup
* add automtls to secrets/auth plugins
* don't remove apiclientmeta parsing
* use formatting directive for fmt.Errorf
* fix ut: remove tls provider func
* remove tlsproviderfunc from backend plugin tests
* use env var to prevent test plugin from running as a unit test
* WIP: remove lazy loading
* move non lazy loaded backend to new package
* use version wrapper for backend plugin factory
* remove backendVersionWrapper type
* implement getBackendPluginType for plugin catalog
* handle backend plugin v4 registration
* add plugin automtls env guard
* modify plugin factory to determine the backend to use
* remove old pluginsets from v5 and log pid in plugin catalog
* add reload mechanism via context
* readd v3 and v4 to pluginset
* call cleanup from reload if non-muxed
* move v5 backend code to new package
* use context reload for for ErrPluginShutdown case
* add wrapper on v5 backend
* fix run config UTs
* fix unit tests
- use v4/v5 mapping for plugin versions
- fix test build err
- add reload method on fakePluginClient
- add multiplexed cases for integration tests
* remove comment and update AutoMTLS field in test
* remove comment
* remove errwrap and unused context
* only support metadatamode false for v5 backend plugins
* update plugin catalog errors
* use const for env variables
* rename locks and remove unused
* remove unneeded nil check
* improvements based on staticcheck recommendations
* use const for single implementation string
* use const for context key
* use info default log level
* move pid to pluginClient struct
* remove v3 and v4 from multiplexed plugin set
* return from reload when non-multiplexed
* update automtls env string
* combine getBackend and getBrokeredClient
* update comments for plugin reload, Backend return val and log
* revert Backend return type
* allow non-muxed plugins to serve v5
* move v5 code to existing sdk plugin package
* do next export sdk fields now that we have removed extra plugin pkg
* set TLSProvider in ServeMultiplex for backwards compat
* use bool to flag multiplexing support on grpc backend server
* revert userpass main.go
* refactor plugin sdk
- update comments
- make use of multiplexing boolean and single implementation ID const
* update comment and use multierr
* attempt v4 if dispense fails on getPluginTypeForUnknown
* update comments on sdk plugin backend
John-Michael Faircloth