Update dependency Flask to v3 (#1986)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [Flask](https://redirect.github.com/pallets/flask)
([changelog](https://flask.palletsprojects.com/changes/)) | major |
`==2.3.3` -> `==3.1.0` |

---

> [!WARNING]
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---

### Release Notes

<details>
<summary>pallets/flask (Flask)</summary>

###
[`v3.1.0`](https://redirect.github.com/pallets/flask/blob/HEAD/CHANGES.rst#Version-310)

[Compare
Source](https://redirect.github.com/pallets/flask/compare/3.0.3...3.1.0)

Released 2024-11-13

-   Drop support for Python 3.8. :pr:`5623`
-   Update minimum dependency versions to latest feature releases.
Werkzeug >= 3.1, ItsDangerous >= 2.2, Blinker >= 1.9. :pr:`5624,5633`
-   Provide a configuration option to control automatic option
    responses. :pr:`5496`
-   `Flask.open_resource`/`open_instance_resource` and
    `Blueprint.open_resource` take an `encoding` parameter to use when
    opening in text mode. It defaults to `utf-8`. :issue:`5504`
- `Request.max_content_length` can be customized per-request instead of
only
    through the `MAX_CONTENT_LENGTH` config. Added
`MAX_FORM_MEMORY_SIZE` and `MAX_FORM_PARTS` config. Added documentation
    about resource limits to the security page. :issue:`5625`
-   Add support for the `Partitioned` cookie attribute (CHIPS), with the
    `SESSION_COOKIE_PARTITIONED` config. :issue:`5472`
- `-e path` takes precedence over default `.env` and `.flaskenv` files.
    `load_dotenv` loads default files in addition to a path unless
    `load_defaults=False` is passed. :issue:`5628`
- Support key rotation with the `SECRET_KEY_FALLBACKS` config, a list of
old
secret keys that can still be used for unsigning. Extensions will need
to
    add support. :issue:`5621`
-   Fix how setting `host_matching=True` or `subdomain_matching=False`
interacts with `SERVER_NAME`. Setting `SERVER_NAME` no longer restricts
    requests to only that domain. :issue:`5553`
- `Request.trusted_hosts` is checked during routing, and can be set
through
    the `TRUSTED_HOSTS` config. :issue:`5636`

###
[`v3.0.3`](https://redirect.github.com/pallets/flask/blob/HEAD/CHANGES.rst#Version-303)

[Compare
Source](https://redirect.github.com/pallets/flask/compare/3.0.2...3.0.3)

Released 2024-04-07

- The default `hashlib.sha1` may not be available in FIPS builds. Don't
access it at import time so the developer has time to change the
default.
    :issue:`5448`
- Don't initialize the `cli` attribute in the sansio scaffold, but
rather in
    the `Flask` concrete class. :pr:`5270`

###
[`v3.0.2`](https://redirect.github.com/pallets/flask/blob/HEAD/CHANGES.rst#Version-302)

[Compare
Source](https://redirect.github.com/pallets/flask/compare/3.0.1...3.0.2)

Released 2024-02-03

-   Correct type for `jinja_loader` property. :issue:`5388`
-   Fix error with `--extra-files` and `--exclude-patterns` CLI options.
    :issue:`5391`

###
[`v3.0.1`](https://redirect.github.com/pallets/flask/blob/HEAD/CHANGES.rst#Version-301)

[Compare
Source](https://redirect.github.com/pallets/flask/compare/3.0.0...3.0.1)

Released 2024-01-18

-   Correct type for `path` argument to `send_file`. :issue:`5336`
- Fix a typo in an error message for the `flask run --key` option.
:pr:`5344`
- Session data is untagged without relying on the built-in `json.loads`
`object_hook`. This allows other JSON providers that don't implement
that.
    :issue:`5381`
-   Address more type findings when using mypy strict mode. :pr:`5383`

###
[`v3.0.0`](https://redirect.github.com/pallets/flask/blob/HEAD/CHANGES.rst#Version-300)

[Compare
Source](https://redirect.github.com/pallets/flask/compare/2.3.3...3.0.0)

Released 2023-09-30

-   Remove previously deprecated code. :pr:`5223`
-   Deprecate the `__version__` attribute. Use feature detection, or
    `importlib.metadata.version("flask")`, instead. :issue:`5230`
-   Restructure the code such that the Flask (app) and Blueprint
    classes have Sans-IO bases. :pr:`5127`
-   Allow self as an argument to url_for. :pr:`5264`
-   Require Werkzeug >= 3.0.0.

</details>

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aws-ts-stackreference-architecture/application/src/backend/requirements.txt

@@ -1,6 +1,6 @@
 Click==8.1.8
 dnspython==2.7.0
-Flask==2.3.3
+Flask==3.1.0
 itsdangerous==2.2.0
 Jinja2==3.1.5
 MarkupSafe>=1.0