CI: GHA conda build & upload

[casperdcl]

Parallel conda builds in 7 minutes on GHA! No more anvil/jenkins.

• add py,np versions to GHA CI conda matrix
  • skip most if on a PR (conserve CI minutes)
• drop recipe/conda_build_config.yaml follow-up windows (CI: windows conda build & release #1918)
• upload to anaconda -c ccpi (on master->dev, on tag->main)
• upload to conda -c https://tomography.stfc.ac.uk/conda (on tag)
  • reindex https://tomography.stfc.ac.uk/conda
• update docs
  • consider deprecating -c ccpi -c https://software.repos.intel.com/python/conda follow-up discussion conda: self-host packages #1870
  • drop jenkins badges
  • pause jenkins CIL GH push trigger
  • pause anvil webhooks
  • update changelog

links

• fixes conda: self-host packages #1870
• part of CI matrices #1598
• part of CI anvil triggering #1560
• related to upgrade build framework #1875
• related to Revert "find_package(Python) (#1842)" #1899 <- find_package(Python) #1842 <- [CMake] using outdated packages for finding Python #1835
• related to Speed up docs action by using build environment from conda build action #1430
• related to Packages ccpi-regulariser tigre cil tomophantom not found during installation. #1416
• related to Distribution: Create a GHA that makes an artifact with conda-pack #1205