Reduce auth chains fetched during v2 state res. (#6952)

The state res v2 algorithm only cares about the difference between auth
chains, so we can pass in the known common state to the `get_auth_chain`
storage function so that it can ignore those events.

1 files changed, 1 insertions, 0 deletions

diff --git a/changelog.d/6952.misc b/changelog.d/6952.misc
new file mode 100644
index 0000000000..e26dc5cab8
--- /dev/null
+++ b/changelog.d/6952.misc
@@ -0,0 +1 @@
+Improve perf of v2 state res for large rooms.