Update Pipeline editor getBlobContent to use graphQL

What does this MR do?

Update Pipeline editor getBlob to use graphQL. We used to have a grapql client resolver to the the blob of a file but under the hood we used REST still. This MR removes the REST call and exclusively use graphql query.

Screenshots (strongly suggested)

No visual changes

Does this MR meet the acceptance criteria?

Conformity

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• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
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• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

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Security

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• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
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