[apache#3285] fix(web): disable the metalake select with only one (ap…

…ache#3385)

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### What changes were proposed in this pull request?
disable the metalake select with only one
<img width="505" alt="image"
src="https://github.com/datastrato/gravitino/assets/9210625/f91df10f-3856-4947-a8cb-6e6cdbe004f3">

### Why are the changes needed?
With only one metalake UI presents user with a choice

Fix: apache#3285

### Does this PR introduce _any_ user-facing change?
N/A

### How was this patch tested?
manual

web/src/app/rootLayout/AppBar.js

@@ -90,6 +90,7 @@ const AppBar = () => {
                       data-refer='select-metalake'
                       value={metalake}
                       label='Metalake'
+                      disabled={store.metalakes.length === 1}
                       sx={{ width: '100%' }}
                     >
                       {metalakes.map(item => {