Support specifying the config location manually (outside of the user's profile)

[Half-Shot]

The intention is for deployments in organizations where a machine may be shared, and the config is not local to a single user. The administrator can then place the common configuration file in a single location for each user to use.

Checklist

• Ensure your code works with manual testing.
• [N/A] New or updated public/exported symbols have accurate TSDoc documentation.
• Linter and other CI checks pass.
• [N/A] I have licensed the changes to Element by completing the Contributor License Agreement (CLA)

[t3chguy]

Related #731

[dbkr]

Would it be possible to find a way to test this? I'm really reluctant to add more stuff like this that will just break without us noticing.

[Half-Shot]

I should be able to write a playwright test for this.

[dbkr]

Amazing, thank you!