fix(openapi/upload): better handling for mismatching files/slugs (#1345)

| 🚥 Resolves CX-2293 |
| :------------------- |

## 🧰 Changes

we previously had a restriction in place where you could not upload a
JSON file (e.g., `petstore.json`) to a slug with a YAML file extension
(e.g., `--slug file.yml`). the reasoning was that we didn't want to
create any unexpected client-side behaviors and we wanted to prioritize
explicitness.

however, we've been getting feedback that it's misleading how `rdme`
directs customers towards certain slugs, only to see an error that they
can't use that slug due to this file extension restriction.

this PR lifts that restriction and makes it so `rdme` will convert a
JSON file to YAML prior to uploading if the slug has a YAML file
extension (or vice versa). it will also emit a warning to the user when
this happens!

## 🧬 QA & Testing

added a bunch of tests for this behavior!

---------

Co-authored-by: Emily Kuo <58803587+emilyskuo@users.noreply.github.com>

Author: kanadgupta

__tests__/commands/openapi/__snapshots__/upload.test.ts.snap

@@ -178,12 +178,40 @@ exports[`rdme openapi upload > given that the API definition is a local file > a
 }
 `;
 
-exports[`rdme openapi upload > given that the API definition is a local file > and the \`--slug\` flag is passed > should handle a slug with a valid but mismatching file extension 1`] = `
+exports[`rdme openapi upload > given that the API definition is a local file > and the \`--slug\` flag is passed > should handle a slug with a valid but mismatching file extension (.json slug, YAML file) 1`] = `
 {
-  "error": [Error: Please provide a valid file extension that matches the extension on the file you provided. Must be \`.json\`, \`.yaml\`, or \`.yml\`.],
+  "result": {
+    "status": "done",
+    "uri": "/branches/1.0.0/apis/custom-slug.json",
+  },
+  "stderr": "- Validating the API definition located at __tests__/__fixtures__/postman/petstore.collection.yaml...
+ ›   Warning: Support for Postman collections is currently experimental.
+ ›   Warning: The file extension in your provided slug (.json) does not match 
+ ›   the file extension of the file you're uploading (.yaml). Your API 
+ ›   definition will be converted to JSON prior to upload.
+- Updating your API definition to ReadMe...
+✔ Updating your API definition to ReadMe... done!
+",
+  "stdout": "🚀 Your API definition (custom-slug.json) was successfully updated in ReadMe!
+",
+}
+`;
+
+exports[`rdme openapi upload > given that the API definition is a local file > and the \`--slug\` flag is passed > should handle a slug with a valid but mismatching file extension (.yml slug, JSON file) 1`] = `
+{
+  "result": {
+    "status": "done",
+    "uri": "/branches/1.0.0/apis/custom-slug.yml",
+  },
   "stderr": "- Validating the API definition located at __tests__/__fixtures__/petstore-simple-weird-version.json...
+ ›   Warning: The file extension in your provided slug (.yml) does not match 
+ ›   the file extension of the file you're uploading (.json). Your API 
+ ›   definition will be converted to YAML prior to upload.
+- Updating your API definition to ReadMe...
+✔ Updating your API definition to ReadMe... done!
+",
+  "stdout": "🚀 Your API definition (custom-slug.yml) was successfully updated in ReadMe!
 ",
-  "stdout": "",
 }
 `;