Allow entries with same user_key for Pushover

[engrbm87]

Breaking change

Proposed change

Pushover allows configuring mutiple applications with different api key. These applications will use the same user key. This PR removes the unique_id so multiple applications (notify services) can be configured.

Type of change

• [ ] Dependency upgrade
• [x] Bugfix (non-breaking change which fixes an issue)
• [ ] New integration (thank you!)
• [ ] New feature (which adds functionality to an existing integration)
• [ ] Deprecation (breaking change to happen in the future)
• [ ] Breaking change (fix/feature causing existing functionality to break)
• [ ] Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #77852
• This PR is related to issue:
• Link to documentation pull request:

Checklist

• [x] The code change is tested and works locally.
• [x] Local tests pass. Your PR cannot be merged unless tests pass
• [x] There is no commented out code in this PR.
• [x] I have followed the development checklist
• [x] The code has been formatted using Black (black --fast homeassistant tests)
• [x] Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• [ ] Documentation added/updated for www.home-assistant.io

If the code communicates with devices, web services, or third-party tools:

• [ ] The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• [ ] New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• [ ] For the updated dependencies - a link to the changelog, or at minimum a diff between library versions is added to the PR description.
• [ ] Untested files have been added to .coveragerc.

The integration reached or maintains the following Integration Quality Scale:

• [ ] No score or internal
• [ ] 🥈 Silver
• [ ] 🥇 Gold
• [ ] 🏆 Platinum

To help with the load of incoming pull requests:

• [ ] I have reviewed two other open pull requests in this repository.

[mdehaas]

@bdraco @frenck May I try to tempt you to include this update in 2022.9.1? Pretty please?

[frenck]

@mdehaas Please... please... don't ping or ask for reviews. This is kinda demanding (even if you didn't mean it like that). Please have patience. Thanks 👍