Add gzip compression for HTML, JS, and CSS files (#999)

## Fixes issue
#996

## Description of Changes
Added gzip compression to HTML, JS, and CSS file responses via the
[`Flask-Compress`
package](https://github.com/colour-science/flask-compress).

Network tab of `http://localhost:3000/department/1` without compression:
<img width="821" alt="Screenshot 2023-07-31 at 12 36 41 PM"
src="https://github.com/lucyparsons/OpenOversight/assets/5885605/1ab41e56-a976-4e3c-83dc-fe3ef0bac16a">

Network tab of `http://localhost:3000/department/1` with compression:
<img width="821" alt="Screenshot 2023-07-31 at 12 32 38 PM"
src="https://github.com/lucyparsons/OpenOversight/assets/5885605/fc09cbec-17b9-4640-9a9d-2348a1b973d3">


## Tests and linting
 - [x] This branch is up-to-date with the `develop` branch.
 - [x] `pytest` passes on my local development environment.
 - [x] `pre-commit` passes on my local development environment.

OpenOversight/app/__init__.py

@@ -5,6 +5,7 @@
 
 from flask import Flask, jsonify, render_template, request
 from flask_bootstrap import Bootstrap
+from flask_compress import Compress
 from flask_limiter import Limiter
 from flask_limiter.util import get_remote_address
 from flask_login import LoginManager
@@ -20,6 +21,7 @@
 
 
 bootstrap = Bootstrap()
+compress = Compress()
 
 login_manager = LoginManager()
 login_manager.session_protection = "strong"
@@ -52,6 +54,7 @@ def create_app(config_name="default"):
     limiter.init_app(app)
     login_manager.init_app(app)
     sitemap.init_app(app)
+    compress.init_app(app)
 
     from OpenOversight.app.main import main as main_blueprint
 

requirements.txt

@@ -21,6 +21,7 @@ email-validator==2.0.0.post2
 Faker==18.13.0
 Flask==2.3.2
 Flask-Bootstrap==3.3.7.1
+Flask-Compress==1.13
 Flask-Limiter==3.3.1
 Flask-Login==0.6.2
 Flask-Migrate==4.0.4