Move usage_graph component to vue_shared folder

What does this MR do?

• Move usage_graph.vue to vue_shared/ allowing it to be used by ee/../storage_counter and app/../projects/storage_counter (will be added in !68866 (merged)).
• Add usage_graph.vue storybook file.

Screenshots or Screencasts (strongly suggested)

How to setup and validate locally (strongly suggested)

1. yarn storybook:install to install storybook's dependencies
2. yarn storybook:start to build and start storybook
3. Navigate to storage_counter -> usage_graph

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have self-reviewed this MR per code review guidelines.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)

Related to #334888