Fix anchor for installing gateway api CRD on getting started Guide

[akankshakumari393]

On this page,the anchor in the link installing-a-gateway-api-bundle does not exist anymore and should be updated to installing-gateway-api

What happened:

What you expected to happen:

How to reproduce it (as minimally and precisely as possible):

Anything else we need to know?:

[akankshakumari393]

/kind documentation

[akankshakumari393]

/assign