Allow to configure TLS versions and ciphers

[manuelluis]

This patch uses 4 new envs:

• DRONE_TLS_MIN_VERSION minimum TLS version that is acceptable
• DRONE_TLS_MAX_VERSION the maximum TLS version that is acceptable
• DRONE_TLS_CURVES list of elliptic curves that will be used in an ECDHE handshake
• DRONE_TLS_CIPHER_SUITES list of supported cipher suites

For example:

DRONE_TLS_MIN_VERSION="TLS12"
DRONE_TLS_CURVES="CurveP256,X25519"
DRONE_TLS_CIPHER_SUITES="ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,ECDHE_RSA_WITH_AES_256_GCM_SHA384,ECDHE_ECDSA_WITH_CHACHA20_POLY1305,ECDHE_RSA_WITH_CHACHA20_POLY1305,ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,ECDHE_RSA_WITH_AES_128_GCM_SHA256"

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[bot2-harness]

This PR has been automatically closed due to inactivity.