Add migration guide

MIGRATION_GUIDE.md

@@ -1,3 +1,89 @@
 # Migration guide
 
-Here you can find migration guides for 
+This document is meant to help you migrate your Terraform config to new newest version. In migration guides we will only 
+describe deprecations or breaking changes and help you to change your configuration to keep the same (or similar) behaviour
+across different versions.
+
+## v0.73.0 ➞ v0.74.0
+### Provider configuration changes
+
+In this change we have done a provider refactor to make it more complete and customizable by supporting more options that 
+were already available in Golang Snowflake driver. This lead to several attributes being added and a few deprecated.
+We will focus on the deprecated ones and show you how to adapt your current configuration to the new changes.
+
+#### *(rename)* username ➞ user
+
+```terraform
+provider "snowflake" {
+  # before
+  username = "username"
+  
+  # after
+  user = "username"
+}
+```
+
+#### *(structural change)* OAuth API
+```terraform
+provider "snowflake" {
+  # before
+  browser_auth        = false
+  oauth_access_token  = "<access_token>"
+  oauth_refresh_token = "<refresh_token>"
+  oauth_client_id     = "<client_id>"
+  oauth_client_secret = "<client_secret>"
+  oauth_endpoint      = "<endpoint>"
+  oauth_redirect_url  = "<redirect_uri>"
+
+  # after
+  authenticator = "ExternalBrowser"
+  token         = "<access_token>"
+  token_accessor {
+    refresh_token   = "<refresh_token>"
+    client_id       = "<client_id>"
+    client_secret   = "<client_secret>"
+    token_endpoint  = "<endpoint>"
+    redirect_uri    = "<redirect_uri>"
+  }
+}
+```
+
+#### *(remove redundant information)* region
+
+Specifying a region is a legacy thing and according to https://docs.snowflake.com/en/user-guide/admin-account-identifier
+you can specify a region as a part of account parameter. Specifying account parameter with the region is also condiered legacy,
+but with this approach it will be easier to convert only your account identifier to the new preferred way of specifying account identifier.
+
+```terraform
+provider "snowflake" {
+  # before
+  region = "<cloud_region_id>"
+
+  # after
+  account = "<account_locator>.<cloud_region_id>"
+}
+```
+
+#### *(todo)* private key path
+
+
+```terraform
+provider "snowflake" {
+  # before
+  private_key_path = "<filepath>"
+
+  # after
+  private_key = file("<filepath>")
+}
+```
+
+#### *(rename)* session_params ➞ params
+```terraform
+provider "snowflake" {
+  # before
+  session_params = {}
+  
+  # after
+  params = {}
+}
+```