hookshot webhook listener moved to /webhook

[HarHarLinks]

fixes #1681, introduced in matrix-org/matrix-hookshot#227

[HarHarLinks]

Upstream hookshot now prefers to listen at /webhook instead of /.
The playbook default is currently to listen on (some common prefix plus) /webhooks, see

matrix-docker-ansible-deploy/roles/matrix-bridge-hookshot/defaults/main.yml

Line 33 in 09412e3

matrix_hookshot_webhook_endpoint: "{{ matrix_hookshot_public_endpoint }}/webhooks"

I think it would be preferable to update our proxied endpoint to match upstream to avoid confusion for new users, but it would be necessary to also be backward-compatible to our old setup in my opinion so admins don't have to manually intervene (set that variable to the old default, or update all their configured services).

This is not a big problem to do with nginx locations, we can simply update the regex to webhooks? to match the s optionally and thus proxy both to the new /webhook endpoint on hookshot side.

However I am not certain on the hookshot side: this variable is used by the playbook to define some config like the following

matrix-docker-ansible-deploy/roles/matrix-bridge-hookshot/defaults/main.yml

Lines 54 to 55 in 09412e3

	matrix_hookshot_github_oauth_endpoint: "{{ matrix_hookshot_webhook_endpoint }}/oauth"
	matrix_hookshot_github_oauth_uri: "https://{{ matrix_server_fqn_matrix }}{{ matrix_hookshot_github_oauth_endpoint }}"

matrix-docker-ansible-deploy/roles/matrix-bridge-hookshot/templates/config.yml.j2

Line 29 in 09412e3

redirect_uri: {{ matrix_hookshot_github_oauth_uri }}

@Half-Shot please advice: I fear that if the playbook's "canonical" default were to be update to /webhook and this hookshot configuration done with this uri, then even though the nginx proxy accepts /webhooks/oauth and forwards it to hookshot, hookshot may not accept it, but only accept /webhook/oauth.

[HarHarLinks]

I may have misunderstood the upstream change, got confused by the exact confusing Half-Shot tried to eliminate. Are GitHub, GitLab, oauth, etc webhooks supposed to go to /webhook now, or still go to / while only generics go to /webhook?

Edit: I received an answer out of band: Half-Shot confirmed the latter. I'll redo the PR entirely at some point.