Sub issue related to #948

[pghildiyal]

Summary

This is task of #948
This particular tickets enables Devtron to add multiple charts so that they can used at the time of creation of application. Allowing user to upload their own charts is out of scope for this task

Proposal

1. User should be able to select chart type if they have yet not selected any chart type
2. If user has selected and saved a chart then user should not be able to change the chart type