Generate migration guide

[lquerel]

Based on the schema diff feature, create a set of Jinja templates to generate migration guides.

See the discussion on the migration guide.

[lmolkova]

Moving this issue to semconv, since weaver can generate diff, it's just semconv part that needs to be done.
It'd probably be great to add some jinja filters/tests in weaver, let's tackle it via separate issues if necessary.