Update FMA contributor docs (#30551)

Updating FMA process for adding new apps by internal and external
contributors. Goals:
- A fast-track experience for contributors if the app does not have
complications (don't need to wait for issue prioritization)
- As few handoffs as possible

---------

Co-authored-by: Ian Littman <iansltx@gmail.com>
Co-authored-by: Marko Lisica <83164494+marko-lisica@users.noreply.github.com>

.github/ISSUE_TEMPLATE/fma-request.md

@@ -0,0 +1,37 @@
+---
+name: 📦 New Fleet-maintained app
+about: Request to add an app to the Fleet-maintained app catalog
+title: 'New FMA: <App Name>'
+labels: ':release,#g-software,fma'
+assignees: 'marko-lisica'
+
+---
+
+### Requestor
+
+- Application name: TODO
+- Application platform: TODO (macOS/Windows)
+
+---
+
+### Validation
+
+- [ ] The following outputs are generated
+        - `/outputs/<app-name>/darwin.json` created
+        - `/outputs/apps.json` updated
+- [ ] Manifest name matches osquery `app.name` (macOS) or `programs.name` (Windows)
+- [ ] Manifest version scheme matches osquery `app.short_bundle_version` (macOS) or `programs.version` (Windows) version scheme
+- [ ] Manifest `unique_identifier` matches osquery `app.bundle_identifier` (macOS only)
+
+### QA
+
+- [ ] App adds successfully to team's library
+- [ ] App installs successfully on host
+- [ ] App opens successfully on host
+- [ ] App uninstalls successfully on host
+
+### Icon
+
+- [ ] Icon added to Figma
+- [ ] Icon added to Fleet
+- [ ] Correct icon appears in the app catalog