chore: Simplify Makefile Architecture

[TeodorSAP]

Description

Changes proposed in this pull request (what was done and why):

• Split general Makefile into sub-makefiles (provision.mk and dependencies.mk)
• Implement .env file, that stores environment variables accessible from both makefiles and shell scripts
• Remove unnecessary make targets (e.g. e2e, upgrade, integration running targets)
• Adapt GitHub actions and scripts that were influenced by the Makefile changes
• Update documentation with necessary ginkgo-cli commands
• Create an ADR with the proposed decisions

Changes refer to particular issues, PRs or documents:

• Resolves Simplify Makefile #740
• Architecture Decision Record (ADR)

Traceability

• The PR is linked to a GitHub issue.
• New features have a milestone set.
• New features have defined acceptance criteria in a corresponding GitHub Issue, and all criteria are satisfied with this PR.
• The corresponding GitHub issue has a respective area and kind label.
• The follow-up issues (if any) are linked in the Related Issues section.
• Adjusted the documentation if the change is user-facing.
• The feature is unit-tested
• The feature is e2e-tested

[NHingerl]

Nice!

If this were user documentation, I'd ask you to adjust the diagrams to match our guidelines. However, I seem to be turning soft with age and I'll just ask you to familiarize yourself with the Kyma diagram guidelines for future diagram draftsmanship.