Implement API endpoint for image alignment

[jonchang]

Description

Implements an API endpoint for the image alignment backend so frontend code can access image alignment features.

Screenshots (if applicable)

Related Issues

#350

Checklist

• The title of this PR is descriptive and concise.
• My changes follow the style guidelines of this project.
• I have added or updated test cases to cover my changes.
• I've let the team know about this PR by linking it in the review channel

Testing notes

Since we still aren't sure about front end work, I tested this by overriding the relevant function in api.ts to also call the image alignment endpoint and used the output of the image alignment endpoint as input to the OCR endpoint. The relevant patch is here:

diff --git a/frontend/api/api.ts b/frontend/api/api.ts
index 0e48b60..ff22eb6 100644
--- a/frontend/api/api.ts
+++ b/frontend/api/api.ts
@@ -28,8 +28,11 @@ export const AlignImage = async (args: AlignImageArgs): Promise<AlignImageRespon
 export const ImageToText = async (args: ImageToTextArgs): Promise<ImageToTextResponse | null> => {
 
     const { sourceImage, templateImage, fieldNames } = args;
+
+    const result = await AlignImage({sourceImage, templateImage});
+
     const form = new URLSearchParams({
-        source_image: sourceImage,
+        source_image: result["result"],
         segmentation_template: templateImage,
         labels: JSON.stringify(fieldNames),
       });