[IMP] general integrations: new gmail plugin link, 19.0 and saas-19.1

[fw-bot]

documentation task card: https://www.odoo.com/odoo/project.task/6001333
main pr: #16823
17.0/18.0 PR: #16824

key change @ gmail.rst lines 8–14:

• add version callout redirecting to master for new plugin

other changes @ outlook.rst lines 9–25:

• add outlook desktop/web callout to match 19.2+
• shuffle version redirect callout down to config section

note: this is one of 3 PRs for the task, due to diffs between 17.0/18.0 ↔ 19.0/saas-19.1

This 19.0 PR can be FWP up to saas-19.1.

Forward-Port-Of: #16825

[robodoo]

[fw-bot]

@huisit cherrypicking of pull request #16825 failed.

stdout:

Auto-merging content/applications/general/integrations/mail_plugins/gmail.rst
Auto-merging content/applications/general/integrations/mail_plugins/outlook.rst
CONFLICT (content): Merge conflict in content/applications/general/integrations/mail_plugins/outlook.rst

Either perform the forward-port manually (and push to this branch, proceeding as usual) or close this PR (maybe?).

In the former case, you may want to edit this PR message as well.

⚠️ after resolving this conflict, you will need to merge it via @robodoo.

More info at https://github.com/odoo/odoo/wiki/Mergebot#forward-port