Openssl3 switch

[hbeni]

Switch to OpenSSL3 for all builds

• linux built natively, dynamically linked

• macOS built natively, dynamically linked

  • This should work at MacOS >= 13 (with libreSSL?), since 12 only ships OSSL 1.1
  • Statically building openssl under macOS is currently unsupported, afaik
  • has a brew receipe for MacOS 10,11,12: https://formulae.brew.sh/formula/openssl@3
    (maybe we should switch to that instead of "selfcompiling our" openssl, so we get more assurance that users can brew install openssl on their systems?)
  • 🆘 🧪 untested, but builds (help wanted: I have no mac to test with!)

• windows 32/64 built with mingw, statically linked

• upgrade the HTTP client too. The linker gives some deprecated warnings already.

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closes #170

[hbeni]

At least builds now.

• ✔️ Linux: loads
• ✔️ Windows: loads
• MacOS: untested, but builds (:sos: help wanted: I have no mac to test with!)

[hbeni]

One thing to think about.... is version incompatibility
It seems MacOS moved from OpenSSL to LibreSSL with 12 ("Ventura", released 24.10.2022).
So if we decide to build against the "shipped" SSL library, we should migrate the build over to libressl instead of the brew thingy.
Doing this will make the affected plugin version incompatible with macOS <12.
⚠️ I'm not yet sure if that openssl->libressl change is just on github, or generally in macOS.

Same seems to be true for linux distros (at least debian, which ships openssl 3 from Debian 12 "bookworm" onwards, which went stable at 10.06.2023)

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ℹ️ Maybe a good solution is to keep this branch up-to-date for some time so we can provide builds against openssl3 on demand. After a while we might merge it and introduce that downward-breaking change to master; which will pin users to the previous release.
ℹ️ ☝️ So a good approach might be to have a release with OpenSSL 1, immediately followed by a release against openssl3; without changing the plugins version number (so the updater does not complain).