Support searching by application instance setting

Currently support staff search for application instances in Metabase. This is for a few reasons:

* The search options in the admin pages aren't rich enough
* The feedback from the pages isn't sufficient to find out what they need to know

Specifically application instance **_settings_** are used in a few distinct ways:

* To indicate recent activity - This is now better handled with `last_launched`
* To query by a specific settings presence or value
* With an intent to change a setting

## Tasks

* [x] https://github.com/hypothesis/lms/issues/5001
* [x] https://github.com/hypothesis/lms/pull/5044
* [x] https://github.com/hypothesis/lms/pull/5050
* [x] https://github.com/hypothesis/lms/pull/5051
* [ ] Some clarity around the settings format field?

## Example journeys

#### Confirming or modifying settings

> Enable JSTOR for a customer

- You’d like to find some application instances so you can:
- Confirm or modify a setting
- You start off in LMS admin pages by searching with:
- Requesters email / domain only
- And the setting you want to know about
- (Optional) And a value you expect the setting to have
- The results you see have the setting specified
- (Optional) If a value was specified they also have the value specified
- You can then click through to the application instance to complete the task

#### Contacting customers with a specific setting

> find all (active) application instances where {"canvas": {"sections_enabled": true}} in order to reach out to them to see if we can have their permission to turn sections_enabled to false

- You’d like to find some application instances so you can:
- Contact all users with a specific setting
- You start off in LMS admin pages by searching with:
- The setting you want to know about
- And a value you expect the setting to have
- The results you see have the setting specified
- And the value specified
- You can see the email addresses of the relevant users in the results to contact them

## Suggested interface

* The page is getting quite cluttered, we may want to break into two columns
* We should have a setting field and setting value field
* If the setting field is populated we will require the path to exist in the settings
* If the value field is populated we will additionally require the value to match
* **Note!** This makes it impossible to search for the value of empty string
* We could present the settings field in a few ways:
* A free text field
* This is good because it can handle anything
* It requires no maintainance
* A drop down
* You can't have a typo
* You don't have to remember the exact setting you want