docs: how to update the OroCommerce piece and the fork

[mikhail-yahorau]

Adds docs/FORK-UPDATE.md, the procedure for building, releasing and installing the orocommerce piece
and for tracking upstream Activepieces in this fork, together with the decision records behind it.

What is changed

• The repo now documents what a release is and how it is identified, the two lanes by which the piece
  reaches an instance, and the re-pinning that a version change requires.
• The recorded build commands are the ones that actually produce the artifact: the previously circulated
  npx nx command is documented as non-functional, along with the two ways the build silently produces a
  wrong artifact.
• docs/decisions/ records the fork's hard-to-reverse calls — nine records, 6 and 7 open, 5 superseded
  by 10.
• §7, taking a new upstream release, stays marked unverified as a whole, and notes that syncs to date
  merged origin/main at an untagged tip rather than an upstream tag.
• Wording is neutral for a public repo: no ticket keys, wiki page ids, person names or internal
  deployment names.

Impact

• No product change: nothing ships to an instance, and no configuration or upgrade step is required.
• The release procedure and the identity of releases 0.3.0 and 1.0.0 become checkable in the repo rather
  than passed on by hand.
• §4's build steps are verified by reproducing both releases byte-for-byte; §7 is asserted, not executed.