docs: shorten help and migration texts to gh-like brevity

Long texts no longer restate the flag list, the instance selection
of tea help environment, the config keys with descriptions or the
team argument rules shown under ARGUMENTS; webhook events come from
services.WebhookEvents; the migration guide refers to tea help
formatting for the terminal layout.

Signed-off-by: bircni <bircni@icloud.com>

internal/app/webhooks.go

@@ -260,11 +260,8 @@ $ tea webhook edit 3 --events push,release --authorization-header-file header.tx
 		command.Args = usageArgs(cobra.MaximumNArgs(1))
 		command.Long = `Create a webhook that delivers events to a URL, by default as JSON for push events.
 
-Events: create, delete, fork, push, issues (every issue event), issues_only, issue_assign,
-issue_label, issue_milestone, issue_comment, pull_request (every pull request event),
-pull_request_only, pull_request_assign, pull_request_label, pull_request_milestone,
-pull_request_comment, pull_request_review, pull_request_sync, pull_request_review_request, wiki,
-repository, release, package, status, workflow_run, workflow_job.
+Events: ` + strings.Join(services.WebhookEvents, ", ") + `; issues and pull_request
+include every issue or pull request event.
 
 Types: ` + strings.Join(services.WebhookTypes, ", ") + `. Slack webhooks need
 --config channel=#name; other types take their settings through --config too.`