Misleading error msg for the start URL on workforce sign-in

## Problem
Pasting the copied start URL from the **Get credentials for [SampleRole]** in the AWS Access portal for a given IAM Identity Center user raises the following input error message: `URLs must start with http:// or https://. Example: https://d-xxxxxxxxxx.awsapps.com/start`.

This error message is quite misleading since the issue that triggered the error message was a hashtag `#` at the end of the start URL. Identifying the issue took some time due to insufficient metadata or guidance from the error message which in this case was a false positive given the pasted URL starts with `https://`.

> ℹ By default, the `#` is included in the start URL copied from the **Get credentials for [SampleRole]** window.
> ℹ Addressing this issue can be an enhancement to support users who retrieve their start URL from the `sso_start_url` property from a local `config` file or the **Get credentials for [SampleRole]** in the AWS Access portal.

## Steps to reproduce the issue
> More clear and verbose steps may be found in this reference [guide](https://docs.aws.amazon.com/sdkref/latest/guide/access-sso.html#idcGettingStarted) under [Step 2].

- Long Version
1. Sign in to the **AWS Access Portal** for a given IAM Identity Center User.
2. Choose the **Access keys** role for an individual user displayed under an AWS Accounts tab.
3. In the **Get Credentials** dialog box, copy the `SSO Start URL` value.
4. In Vs Code, launch the command palette `Shift+Command+P (Ctrl+Shift+P Windows)` then run the `AWS: Add a New Connection` command.
5. Choose the **Workforce** sign-in option and select continue.
6. Paste the copied `SSO Start URL` value into the **Start URL** field.
7. Observe the error message displayed on the pasted value.

- Short Version
1. In Vs Code, launch the command palette `Shift+Command+P (Ctrl+Shift+P Windows)` then run the `AWS: Add a New Connection` command.
2. Choose the **Workforce** sign-in option and select continue.
3. Paste the value `https://d-xxxxxxxxxx.awsapps.com/start/#` into the **Start URL** field.
4. Observe the error message displayed on the pasted value.

## Expected behavior
The `SSO Start URL` value copied from the AWS Access Portal should not trigger an error message. A more _semantic_ message may be displayed to better guide the user on the specific issue. The error message can further be enhanced by informing a user that, for example, the start URL must also explicitly be in the following format: `https://d-xxxxxxxxxx.awsapps.com/start`, in addition to the pre-existing requirement: `URLs must start with http:// or https:// ...`.

## System details
> Retrieved from running: `AWS: About`

- OS: Linux x64 5.15.153.1-microsoft-standard-WSL2
- Visual Studio Code version: 1.92.0-insider
- AWS Toolkit version: 3.20.0

Start with the AWS: Add a New Connection command and its Workforce sign-in flow, then reproduce the issue using the copied SSO Start URL ending in #. Done when that portal value no longer triggers a misleading URL-scheme error, or the validation clearly identifies the specific URL problem and required format.

Written by the indexing model from the issue text.