chore(docs): Add more godoc to important APIs (#118)

As part of the v2 release we want to improve documentation for developers and for our plugin-sdk. 

Right now we have a bit of mix-match of tutorials and docs https://www.cloudquery.io/docs/developers/sdk/provider/configuration

What we want to achieve:
- SDK documentation in godoc together with docs - https://pkg.go.dev/github.com/cloudquery/plugin-sdk
- Tutorials - https://www.cloudquery.io/docs/developers/sdk/overview

There is still much more documentation to be added with some more examples but this should be a good start.

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Explain what problem this PR addresses
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Author: yevgenypats

README.md

@@ -1,17 +1,16 @@
-CloudQuery Plugin SDK ![License](https://img.shields.io/github/license/cloudquery/cloudquery?style=flat-square)
-=======================
+# CloudQuery Plugin SDK
 
-This SDK enables building CloudQuery plugins which allows CloudQuery's users to extract/load/transform existing and popular service providers as well as custom in-house solutions into a SQL Database.
+CloudQuery SDK enables building CloudQuery source and destination plugins.
 
-CloudQuery itself is a tool that transforms your cloud infrastructure into queryable SQL for easy monitoring, governance and security. You can find more about CloudQuery on its website and its GitHub repository.
+Source plugins allows developers to extract information from third party APIs and enjoying built-in transformations, concurrency, logging, testing and database agnostic support via destination plugins.
 
+Destinations plugins allows writing the data from any of the source plugins to an additional database, message queue, storage or any other destination without recompiling any of the source plugins.
 
 ## Getting Started & Documentation
 
-* Homepage: https://cloudquery.io
-* Releases: https://github.com/cloudquery/cloudquery/releases
-* Documentation: https://docs.cloudquery.io
-* Database Configuration: https://docs.cloudquery.io/database-configuration
+- Homepage: https://cloudquery.io
+- Releases: https://github.com/cloudquery/cloudquery/releases
+- Documentation: https://docs.cloudquery.io
 
 ## Supported plugins
 

clients/doc.go

@@ -0,0 +1,3 @@
+// package clients is a wrapper around grpc clients so clients can work
+// with non protobuf structs and handle unmarshaling
+package clients

clients/source.go

@@ -1,5 +1,3 @@
-// package clients is a wrapper around grpc clients so clients can work
-// with non protobuf structs and handle unmarshaling
 package clients
 
 import (
@@ -14,6 +12,7 @@ import (
 	"google.golang.org/grpc"
 )
 
+// SourceClient
 type SourceClient struct {
 	pbClient pb.SourceClient
 }

codegen/doc.go

@@ -1,2 +1,2 @@
-// codgen helps autogenerate cloudquery plugins configured by definition
+// Package codgen helps autogenerate tables for CloudQuery source plugins from Go structs (of relevant SDKs)
 package codegen

codegen/golang.go

@@ -156,6 +156,7 @@ func (t *TableDefinition) addColumnFromField(field reflect.StructField, parentFi
 	t.Columns = append(t.Columns, column)
 }
 
+// NewTableFromStruct creates a new TableDefinition from a struct by inspecting its fields
 func NewTableFromStruct(name string, obj interface{}, opts ...TableOptions) (*TableDefinition, error) {
 	t := &TableDefinition{
 		Name:            name,

plugins/docs.go

@@ -0,0 +1,2 @@
+// Package plugins defines APIs for source and destination plugins
+package plugins

plugins/source.go

@@ -59,6 +59,8 @@ func addInternalColumns(tables []*schema.Table) {
 	}
 }
 
+// NewSourcePlugin returns a new plugin with a given name, version, tables, newExecutionClient
+// and additional options.
 func NewSourcePlugin(name string, version string, tables []*schema.Table, newExecutionClient SourceNewExecutionClientFunc, opts ...SourceOption) *SourcePlugin {
 	p := SourcePlugin{
 		name:               name,
@@ -91,27 +93,32 @@ func (p *SourcePlugin) validate() error {
 	return nil
 }
 
+// Tables returns all supported tables by this source plugin
 func (p *SourcePlugin) Tables() schema.Tables {
 	return p.tables
 }
 
+// ExampleConfig returns an example configuration for this source plugin
 func (p *SourcePlugin) ExampleConfig() string {
 	return p.exampleConfig
 }
 
+// Name return the name of this plugin
 func (p *SourcePlugin) Name() string {
 	return p.name
 }
 
+// Version returns the version of this plugin
 func (p *SourcePlugin) Version() string {
 	return p.version
 }
 
+// SetLogger sets the logger for this plugin which will be used in Sync and all other function calls.
 func (p *SourcePlugin) SetLogger(log zerolog.Logger) {
 	p.logger = log
 }
 
-// Sync data from source to the given channel
+// Sync is syncing data from the requested tables in spec to the given channel
 func (p *SourcePlugin) Sync(ctx context.Context, spec specs.Source, res chan<- *schema.Resource) error {
 	c, err := p.newExecutionClient(ctx, p.logger, spec)
 	if err != nil {

schema/doc.go

@@ -0,0 +1,2 @@
+// Package schema defines types supported by tables in source plugins
+package schema

serve/doc.go

@@ -1,3 +1,4 @@
+// Package serve defines APIs to serve (invoke) source and destination plugins
 package serve
 
 import (

specs/doc.go

@@ -0,0 +1,3 @@
+// Package specs specs for source and destination plugins including
+// parsers and readers.
+package specs