Differentiate Amplify Gen 1 CLI Custom AWS resources from Amplify Libraries section

**Is your feature request related to a problem? Please describe.**
[Custom AWS resources](https://docs.amplify.aws/gen1/javascript/tools/cli/custom/) section is related to Amplify CLI Gen 1 and independent of Amplify Library versions (Like JS v5/v6 , Android v1/v2 etc.). The current doc seems to create confusion that custom resources are a JS v6 or Android v2 only feature (custom resources section does not come up [here](https://docs.amplify.aws/gen1/react/prev/build-a-backend/)) which is not true

**Describe the solution you'd like**
Distinction between Library specific sections and CLI sections. Custom resources section should be accessible without being dependent on library version

**Describe alternatives you've considered**
N/A

**Additional context**
N/A