Updated major packages and support for OpenSSL 3+

[maricavor]

Changes

• Platform & dependencies

Require OTP 26+ and build/test on Debian bookworm with OpenSSL 3 (Dockerfiles, docker-compose.yml, .tool-versions, README).
Upgrade hackney to ~> 4.0 and lager to 3.9.2 (OTP 26–compatible).
Refresh rebar.lock and document build/test commands in README and COMMANDS.

• Hackney 4.0 compatibility

epp_http_client: adapt to hackney 4’s response shape — body is returned in {ok, StatusCode, Headers, Body}; remove call to removed hackney:body/1.
Fixes EPP worker crashes after successful HTTP responses from the Rails epp app (e.g. XML Console poll/login returning EPP XML).

• TLS: optional client certificates

Add require_client_certs application env (default true — unchanged production behavior).
When false, TLS clients may connect without a client cert; certs are still verified if presented (fail_if_no_peer_cert follows the setting).
Document in README; add tls_client_optional_cert_SUITE and acceptor restart helper so env changes take effect (listen options are fixed at acceptor init).
Note: changing this at runtime requires restarting epp_tls_acceptor.

• Build & CI

Move rebar3_appup_plugin and appup hooks to the prod profile only so rebar3 as test compile in GitHub Actions does not fail on .appup.src evaluation.
Set application version in epp_proxy.app.src to 0.1.0 (was literal "git", which broke appup when git metadata was unavailable in CI).