CSI `CreateVolume` RPC is idempotent given that the topology,
capabilities, and parameters are unchanged. CSI volumes have many
user-defined fields that are immutable once set, and many fields that
are not user-settable.
Update the `Register` RPC so that updating a volume via the API merges
onto any existing volume without touching Nomad-controlled fields,
while validating it with the same strict requirements expected for
idempotent `CreateVolume` RPCs.
Also, clarify that this state store method is used for everything, not just
for the `Register` RPC.
* command/csi: csi, csi_plugin, csi_volume
* helper/funcs: move ExtraKeys from parse_config to UnusedKeys
* command/agent/config_parse: use helper.UnusedKeys
* api/csi: annotate CSIVolumes with hcl fields
* command/csi_plugin: add Synopsis
* command/csi_volume_register: use hcl.Decode style parsing
* command/csi_volume_list
* command/csi_volume_status: list format, cleanup
* command/csi_plugin_list
* command/csi_plugin_status
* command/csi_volume_deregister
* command/csi_volume: add Synopsis
* api/contexts/contexts: add csi search contexts to the constants
* command/commands: register csi commands
* api/csi: fix struct tag for linter
* command/csi_plugin_list: unused struct vars
* command/csi_plugin_status: unused struct vars
* command/csi_volume_list: unused struct vars
* api/csi: add allocs to CSIPlugin
* command/csi_plugin_status: format the allocs
* api/allocations: copy Allocation.Stub in from structs
* nomad/client_rpc: add some error context with Errorf
* api/csi: collapse read & write alloc maps to a stub list
* command/csi_volume_status: cleanup allocation display
* command/csi_volume_list: use Schedulable instead of Healthy
* command/csi_volume_status: use Schedulable instead of Healthy
* command/csi_volume_list: sprintf string
* command/csi: delete csi.go, csi_plugin.go
* command/plugin: refactor csi components to sub-command plugin status
* command/plugin: remove csi
* command/plugin_status: remove csi
* command/volume: remove csi
* command/volume_status: split out csi specific
* helper/funcs: add RemoveEqualFold
* command/agent/config_parse: use helper.RemoveEqualFold
* api/csi: do ,unusedKeys right
* command/volume: refactor csi components to `nomad volume`
* command/volume_register: split out csi specific
* command/commands: use the new top level commands
* command/volume_deregister: hardwired type csi for now
* command/volume_status: csiFormatVolumes rescued from volume_list
* command/plugin_status: avoid a panic on no args
* command/volume_status: avoid a panic on no args
* command/plugin_status: predictVolumeType
* command/volume_status: predictVolumeType
* nomad/csi_endpoint_test: move CreateTestPlugin to testing
* command/plugin_status_test: use CreateTestCSIPlugin
* nomad/structs/structs: add CSIPlugins and CSIVolumes search consts
* nomad/state/state_store: add CSIPlugins and CSIVolumesByIDPrefix
* nomad/search_endpoint: add CSIPlugins and CSIVolumes
* command/plugin_status: move the header to the csi specific
* command/volume_status: move the header to the csi specific
* nomad/state/state_store: CSIPluginByID prefix
* command/status: rename the search context to just Plugins/Volumes
* command/plugin,volume_status: test return ids now
* command/status: rename the search context to just Plugins/Volumes
* command/plugin_status: support -json and -t
* command/volume_status: support -json and -t
* command/plugin_status_csi: comments
* command/*_status: clean up text
* api/csi: fix stale comments
* command/volume: make deregister sound less fearsome
* command/plugin_status: set the id length
* command/plugin_status_csi: more compact plugin health
* command/volume: better error message, comment
