mgr/dashboard: allow tls 1.2 with a config option

mgr/dashboard: allow tls 1.2 with a config option

Provide the option to allow tls1.2

`ceph dashboard set-enable-unsafe-tls-v1-2 True` followed with a mgr
restart will enable tls 1.2.

With tls1.2 enabled
```
╰─$ nmap -sV --script ssl-enum-ciphers -p 11000 127.0.0.1
Starting Nmap 7.93 ( https://nmap.org ) at 2023-09-27 16:56 IST
Nmap scan report for localhost (127.0.0.1)
Host is up (0.00018s latency).

PORT      STATE SERVICE  VERSION
11000/tcp open  ssl/http CherryPy wsgiserver
|_http-server-header: Ceph-Dashboard
| ssl-enum-ciphers:
|   TLSv1.2:
|     ciphers:
|       TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (ecdh_x25519) - A
|       TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256 (ecdh_x25519) - A
|       TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (ecdh_x25519) - A
|       TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256 (ecdh_x25519) - A
|       TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA (ecdh_x25519) - A
|       TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA (ecdh_x25519) - A
|       TLS_RSA_WITH_AES_256_GCM_SHA384 (rsa 2048) - A
|       TLS_RSA_WITH_AES_256_CCM (rsa 2048) - A
|       TLS_RSA_WITH_AES_128_GCM_SHA256 (rsa 2048) - A
|       TLS_RSA_WITH_AES_128_CCM (rsa 2048) - A
|       TLS_RSA_WITH_AES_256_CBC_SHA256 (rsa 2048) - A
|       TLS_RSA_WITH_AES_128_CBC_SHA256 (rsa 2048) - A
|       TLS_RSA_WITH_AES_256_CBC_SHA (rsa 2048) - A
|       TLS_RSA_WITH_AES_128_CBC_SHA (rsa 2048) - A
|     compressors:
|       NULL
|     cipher preference: server
|   TLSv1.3:
|     ciphers:
|       TLS_AKE_WITH_AES_256_GCM_SHA384 (ecdh_x25519) - A
|       TLS_AKE_WITH_CHACHA20_POLY1305_SHA256 (ecdh_x25519) - A
|       TLS_AKE_WITH_AES_128_GCM_SHA256 (ecdh_x25519) - A
|       TLS_AKE_WITH_AES_128_CCM_SHA256 (ecdh_x25519) - A
|     cipher preference: server
|_  least strength: A

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 16.55 seconds
```

Without tls1.2 enabled (which defaults to tls 1.3)
```
╰─$ nmap -sV --script ssl-enum-ciphers -p 11000 127.0.0.1
Starting Nmap 7.93 ( https://nmap.org ) at 2023-09-27 16:54 IST
Nmap scan report for localhost (127.0.0.1)
Host is up (0.000075s latency).

PORT      STATE SERVICE  VERSION
11000/tcp open  ssl/http CherryPy wsgiserver
| ssl-enum-ciphers:
|   TLSv1.3:
|     ciphers:
|       TLS_AKE_WITH_AES_256_GCM_SHA384 (ecdh_x25519) - A
|       TLS_AKE_WITH_CHACHA20_POLY1305_SHA256 (ecdh_x25519) - A
|       TLS_AKE_WITH_AES_128_GCM_SHA256 (ecdh_x25519) - A
|       TLS_AKE_WITH_AES_128_CCM_SHA256 (ecdh_x25519) - A
|     cipher preference: server
|_  least strength: A
|_http-server-header: Ceph-Dashboard
```

Fixes: https://tracker.ceph.com/issues/62940
Signed-off-by: Nizamudeen A <nia@redhat.com>
(cherry picked from commit 219c62bea60083c0e59a86454b0cecf8afaf9780)