INT-578 Use PVC by default for all DB branching

[vladrbg]

No description provided.

[linear-code]

INT-578

[greptile-apps]

Greptile Summary

This PR documents PVC-backed storage as the default for database branches beginning with operator 3.191.0, motivated by reducing reliance on node-local capacity.

• Explains the release-boundary changes to storage and memory defaults.
• Adds Helm examples for PVC sizing, StorageClass selection, and emptyDir opt-out.
• Documents fallback and explicit-volume precedence behavior.

Important Files Changed

Filename	Overview
docs/sharing-the-cluster/db-branching.md	Adds the new PVC storage guidance, but its no-change upgrade claim conflicts with the documented scope of legacy volume-limit settings.

Prompt To Fix All With AI

### Issue 1
docs/sharing-the-cluster/db-branching.md:153
**Legacy volume limits stop applying**

When upgrading with explicit `initPodVolumeLimit` or `databasePodVolumeLimit` values but no `emptyDir` opt-out, the new default PVC path stops consuming those settings and instead uses the 20Gi PVC defaults, causing branches configured for larger databases to run out of volume space despite the claim that every explicit setting keeps its meaning.

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

_{Reviews (1): Last reviewed commit: "pvc" | Re-trigger Greptile}

[greptile-apps]

Legacy volume limits stop applying

When upgrading with explicit initPodVolumeLimit or databasePodVolumeLimit values but no emptyDir opt-out, the new default PVC path stops consuming those settings and instead uses the 20Gi PVC defaults, causing branches configured for larger databases to run out of volume space despite the claim that every explicit setting keeps its meaning.

Prompt To Fix With AI

This is a comment left during a code review.
Path: docs/sharing-the-cluster/db-branching.md
Line: 153

Comment:
**Legacy volume limits stop applying**

When upgrading with explicit `initPodVolumeLimit` or `databasePodVolumeLimit` values but no `emptyDir` opt-out, the new default PVC path stops consuming those settings and instead uses the 20Gi PVC defaults, causing branches configured for larger databases to run out of volume space despite the claim that every explicit setting keeps its meaning.

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.