[FIX] website_slides: Google drive does not start (error message)

Issue

	- Install "Elearning" module
	- Activate "Drive" credidentials in settings
	- Go to any course and edit it.
	- In "Content" tab, click on "Add Content"
	- Select `Video` as 'Type'
	- Copy/Paste the Google Drive video link in "Document URL" field
	- Wait for other field to be computed then "Save & Close"
	- Save the course
	- Go to the website to watch this new content

	Youtube error message

Cause

	'mime_type' field is readonly. When saving the course (slide.channel),
	the slide is not saved yet, and therefore drop the 'mime_type' value.
	When generating the `embed url`, it verify if a mime_type is set: if not,
	it will generate an iframe with youtube.com as domain, else,
	a drive.google.com domain.

Solution

	Add `force_save="1"` on `mime_type` field.

opw-2294344

closes odoo/odoo#59863

Signed-off-by: bon-odoo <nboulif@users.noreply.github.com>

addons/website_slides/views/slide_slide_views.xml

@@ -68,7 +68,7 @@
                                             'required': [('slide_type', 'in', ('video'))],
                                             'invisible': [('slide_type', 'not in', ('video'))]}" />
                                         <field name="document_id" invisible="1"/>
-                                        <field name="mime_type" readonly="1" groups="base.group_no_one"/>
+                                        <field name="mime_type" force_save="1" readonly="1" groups="base.group_no_one"/>
                                         <field name="datas" string="Attachment"
                                             attrs="{'invisible': [('slide_type', 'not in', ('document', 'presentation'))]}"/>
                                     </group>