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> |