refactor!: update Kind field to Type in source code (#2312)

Update source code `Kind` to `Type`. It's only changes within our code.
Changes to yaml tag (that will affect users) will be done in later PRs.

This is a breaking change since it updates telemetry's span attribute
from `source_kind` to `source_type`.

Related #817

Future updates will include: 
* Updating a preprocessing function to convert config file from v1 to v2
* Update unmarshal function for ToolsFile to convert config file (test
will fail since the yaml tag is not yet updated).
* Update yaml tag (test will pass).

internal/tools/cloudsql/cloudsqlcreatebackup/cloudsqlcreatebackup_test.go

@@ -46,7 +46,7 @@ func TestParseFromYaml(t *testing.T) {
 			want: server.ToolConfigs{
 				"create-backup-tool": cloudsqlcreatebackup.Config{
 					Name:         "create-backup-tool",
-					Kind:         "cloud-sql-create-backup",
+					Type:         "cloud-sql-create-backup",
 					Description:  "a test description",
 					Source:       "a-source",
 					AuthRequired: []string{},