Refactor SlackWebhookHook in order to use slack_sdk instead of HttpHook methods

[Taragolis]

Fundamental refactor of SlackWebhookHook with breaking changes.
I tried to minimise breaking changes, however main (and hope the only once) braking change SlackWebhookHook not anymore inherit from airflow.providers.http.hooks.http.HttpHook anymore and use slack_sdk.WebhookClient instead

Additional changes:

1. Warn user that it is not safe to specify webhook token (url) directly in the Hook and suggest to switch to Airflow Connections.
2. Deprecate specify webhook message attribute in __init__ method and mainly use hook attributes only for configure slack_sdk.WebhookClient. It is still possible to set as Hook arguments.
3. Inform users (always) that it is not possible to change channel, username and icon by use Slack Incoming Webhook. Users might previously use for two reasons:
   a. Hook and Operators not cover this part
   b. Hook initially created for use with Legacy Incoming Webhooks based on Slack Integration
4. Change SlackWebhookHook arguments in Operators
5. Add documentation for Slack Incoming Webhook connection type

Fundamental also mean that main files related to SlackWebhookHook (airflow/providers/slack/hooks/slack_webhook.py,
tests/providers/slack/hooks/test_slack_webhook.py) re-created from scratch

[Taragolis]

Even with this PR it is not possible to get rid of apache-airflow-providers-http dependency.
Mainly because SlackWebhookOperator inherit from SimpleHttpOperator

airflow/airflow/providers/slack/operators/slack_webhook.py

Lines 28 to 30 in 706a618

	class SlackWebhookOperator(SimpleHttpOperator):
	"""

But actually it not use any feature of SimpleHttpOperator just because it overwrite execute method where all internal stuff of SimpleHttpOperator happen.

Changes in SlackWebhookOperator could be done after this PR. In fact this PR contain a lot of changes so it would be difficult to track changes if it done in single PR.

airflow/airflow/providers/slack/operators/slack_webhook.py

Lines 94 to 110 in 706a618

	def execute(self, context: Context) -> None:
	"""Call the SlackWebhookHook to post the provided Slack message"""
	self.hook = SlackWebhookHook(
	self.http_conn_id,
	self.webhook_token,
	self.message,
	self.attachments,
	self.blocks,
	self.channel,
	self.username,
	self.icon_emoji,
	self.icon_url,
	self.link_names,
	self.proxy,
	)
	self.hook.execute()

[potiuk]

Slack seems to be a beast - can you plese rebase :) ?

[potiuk]

BTW. Thanks from trying to unentangle the mess :D

[Taragolis]

Another option create separate methods send_legacy and send_text_legacy which allow send to Legacy Incoming Webhook without any warnings, might be helpful if there is no possible for user change Legacy Incoming Webhook.

[potiuk]

Is there are good reason why it would not be possible, or just " I had no time to change it?". If that's the latter, then this is no problem to have warnings. Warnings are there to be annoying enough to gently push the user to get rid of the legacy code and make investment in doing so. The only reason for allowing to silence warnings easily is when there migtht be really good reasons and use cases that cannot be handled with the "new way" of doing things.

[Taragolis]

Only one case when user do not have access to create new applications in slack workspace.
One day Slack Webhook based on Slack integrations will be removed anyway so in user perspective better started to migrated from legacy service to 2 successors: Slack API and Slack Incoming Webhook based on API/App

This might be the later feature if someone requested it and better warn user right now always.

[potiuk]

@Taragolis - are you working on making some of the changes discussed ? I am gearing up to prepare a new provider's wave, so it would be great to merge this one before.

[Taragolis]

@Taragolis - are you working on making some of the changes discussed ? I am gearing up to prepare a new provider's wave, so it would be great to merge this one before.

Yep. Plan to finish changes by today

[Taragolis]

Finally all checks passed. Today it takes a bit longer rather than usual.

[potiuk]

Nice refactor!