docs: add Tencent Cloud webhook provider to registry (#6432)

Add external-dns-tencentcloud-webhook to the webhook provider
table in README.md. Supports DNSPod (public) and PrivateDNS
(VPC-scoped) with static credentials or OIDC (TKE RRSA).

Author: QianChenglong

README.md

@@ -117,6 +117,7 @@ from the usage of any externally developed webhook.
 | SAKURA Cloud          | https://github.com/sacloud/external-dns-sacloud-webhook              |
 | Simply                | https://github.com/uozalp/external-dns-simply-webhook                |
 | STACKIT               | https://github.com/stackitcloud/external-dns-stackit-webhook         |
+| Tencent Cloud         | https://github.com/tkestack/external-dns-tencentcloud-webhook        |
 | Unbound               | https://github.com/guillomep/external-dns-unbound-webhook            |
 | Unifi                 | https://github.com/kashalls/external-dns-unifi-webhook               |
 | UniFi                 | https://github.com/lexfrei/external-dns-unifios-webhook              |