Set East US as the only proposed region to run azd up (#367)

Based on the feedback of issue 344
(#344),
EastUS should be the only proposed region.

## Purpose
Set East US as the default proposed region to deploy all the services.
Based on the feedback

## Does this introduce a breaking change?
<!-- Mark one with an "x". -->
```
[ ] Yes
[X] No
```

## Pull Request Type
What kind of change does this Pull Request introduce?

<!-- Please check the one that applies to this PR using "x". -->
```
[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[X] Documentation content changes
[ ] Other... Please describe:
```

## How to Test
*  Get the code

```
git clone [repo-address]
cd [repo-name]
```
run `azd up`

Update nuget pkgs, update deploy to use gpt-4o-mini and target region (…

…#358)

## Purpose

- update nuget packages to latest versions
- change default model from `gpt-35-turbo` to `gpt-4o-mini`
- change default azure deployment region to `East US`
- remove the paragraph about requesting access to `AOAI`

## Does this introduce a breaking change?
<!-- Mark one with an "x". -->
```
[ ] Yes
[X] No
```

## Pull Request Type
What kind of change does this Pull Request introduce?

<!-- Please check the one that applies to this PR using "x". -->
```
[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[X] Refactoring (no functional changes, no api changes)
[X] Documentation content changes
[X] Other: Update deploy to use the latest AOAI GPT model
```

## How to Test
*  Get the code

```
git clone [repo-address]
cd [repo-name]
```

* Test the code / deploy
```
azd up
```