doc: rename the startup performance initiative to startup snapshot (#47111)

The initiative has been more focused on startup snapshot integration
which is more of a feature on its own, so rename it to "startup
snapshot".
Background: we are also considering adding a more generic performance
initiative in nodejs/TSC#1343.

Author: joyeecheung

doc/contributing/strategic-initiatives.md

@@ -11,7 +11,7 @@ agenda to ensure they are active and have the support they need.
 | Core Promise APIs |[Antoine du Hamel][aduh95]|<https://github.com/nodejs/TSC/issues/1094>|
 | QUIC / HTTP3 |[James M Snell][jasnell]|<https://github.com/nodejs/quic>|
 | Shadow Realm |[Chengzhong Wu][legendecas]|<https://github.com/nodejs/node/issues/42528>|
-| Startup performance|[Joyee Cheung][joyeecheung]|<https://github.com/nodejs/node/issues/35711>|
+| Startup Snapshot |[Joyee Cheung][joyeecheung]|<https://github.com/nodejs/node/issues/35711>|
 | V8 Currency |[Michaël Zasso][targos]||
 | Next-10 |[Michael Dawson][mhdawson]|<https://github.com/nodejs/next-10>|
 | Single executable apps |[Darshan Sen][RaisinTen]|<https://github.com/nodejs/node/issues/43432>|