Use Conan for installing dependencies

[SJaffa]

Starting from the development branch, first issue was the same spdlog error as in sopt

• Update install instructions in README.md with Use Conan for installing dependencies #302 (comment)
• Fix code errors in algo_factory.h
• Only include sopt TF headers from algo_factory.h when cppflow==on option is passed to cmake
• In sopt, move class GProximal to the sopt::algorithm namespace
• Update documentation GitHub Actions workflow

[SJaffa]

• Checks fail
  • All Ubuntu fails in build step because of spdlog error in SOPT, need to pull SOPT to fix this
  • macOS clang also fails in build step because of spdlog error
  • macOS gcc fails in 'install conan on gcc'
    • boost fiber error:

boost/1.78.0: WARN: Boost component 'fiber' is missing libraries. Try building boost with '-o boost:without_fiber'. (Option is not guaranteed to exist) ERROR: boost/1.78.0: Error in package_info() method, line 1592 raise ConanException("These libraries were expected to be built, but were not built: {}".format(non_built)) ConanException: These libraries were expected to be built, but were not built: {'boost_fiber'}

[tkoskela]

We need to close astro-informatics/sopt#279 before we can make progress with this

[mmcleod89]

Looking at things here I think that this is up to date now with what I expect, keeping the forward-backward tensorflow test out of it for a separate PR. 👍

[tkoskela]

Ok, from my point of view the only outstanding item is updating the documentation workflow. I think everything else looks good to go.

[SJaffa]

I've checked the installation instructions in the readme work for me from a clean setup, I've updated the documentation workflow (although not tested this as it only runs when we push to development branch) and the other couple of outdated bits in the readme I've made new issues as they can be solved separately. So if someone could check over the docs workflow I think this is finally ready to merge! (assuming the tests pass...)

[mmcleod89]

C++ code is good for me; as far as the docs action goes it looks okay to me but I don't think it's possible to run it manually so I'm happy for there to be a separate issue if there needs to be a further tweak there rather than extending this PR any further.

All conversations from the review have now been marked resolved and TK has said he's happy to merge.