Allow ptb and canary webhooks for discord integration
What does this MR do and why?
Allow ptb and canary webhooks for discord integration
When a discord user uses one of their testing clients (ptb or canary) the client will give the user webhook urls that point to the backend that is used by that client. A ptb client will copy a webhook url pointing to ptb.discord.com and a canary client will copy a url that points to canary.discord.com. Only the stable client is pointing to discord.com without subdomain.
Given that both subdomains are valid domains for discord webhooks, the validation should allow them, so users don't have to manually strip out the subdomains from the url.
Both testing clients are documented at https://support.discord.com/hc/en-us/articles/360035675191-Discord-Testing-Clients
References
Screenshots or screen recordings
No UI changes
How to set up and validate locally
Verify that you can create a discord integration that has the webhook pointing to discord.com, ptb.discord.com or canary.discord.com
MR acceptance checklist
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