guide: branching strategies

Diagrams and guide for collaborative branching strategies (e.g. using `cml pr` for experiments in a large team, reporting, rebase vs squash-merging, hiding unneeded rows in Studio, etc.)

Also saving results https://stackoverflow.com/a/74563657/3896283

Also should mention caveats (e.g. cascading/nested PRs obscures reports).

Related resources:

- https://stackoverflow.com/a/70205896
- https://github.com/iterative/viewer/issues/3157
- https://github.com/iterative/example-get-started/pull/31
- https://discord.com/channels/485586884165107732/1073560646718849034/1073586419907448933 (`on: workflow_dispatch`, `commit message [skip-ci]`, `if: contains(github.event.head_commit.message, '[trigger]')`)

Related issues (potentially duplicates and/or sub-issues):

- [x] https://github.com/iterative/cml/issues/656
- [ ] https://github.com/iterative/cml/issues/1126
- [ ] #393
- [ ] #390