feat: add compatibility check and health diagnostics compat feature

[vickyyyyyyy]

Issue: #38 - please read, there is a lot of context and screenshots which may help 🙏

Supports the old format of error messages for users running Grafana <8, even when we have a new backend response coming from the plugin (for Grafana 8+).

Overriding the testDatasource function allows us to keep the new backend response and new core Grafana UI as it is for the new changes, but allow support for transforming what we send back from our plugin to core Grafana. This should improve maintainability.

Takes inspriration from https://github.com/marcusolsson/grafana-plugin-support/blob/c3f0272005d2e68142a756dbd85ad2df1ccbb962/src/utils/capability.ts

The addition of the new compatibility.ts and compatFeatures.ts files should also help us with similar issues in the future for easier maintainability for knowing what compatibility issues we have. These can also be shared across all our plugins, rather than requiring copypasta in each individual plugin.

Usage:

From the plugin's datasource.ts file:

import { healthDiagnosticsErrorsCompat } from 'ui-enterprise';

async testDatasource() {
    return healthDiagnosticsErrorsCompat(super.testDatasource.bind(this))
}

Before

Grafana <8:

With no support for backwards compatibility, users would see an error message that is not useful:

Grafana 8+:

After

Grafana <8:

They can now see the same old format and the new changes do not affect it:

Grafana 8+:

[scottlepp]

using "test" is a bit confusing to me. i assume its a unit test. can we use "check" or some other term?

[scottlepp]

checkDatasource? testDatasource is confusing to me, I assume its a unit test

[vickyyyyyyy]

this is the function we want to override the core Grafana's testDatasource with: https://github.com/grafana/grafana/blob/master/packages/grafana-runtime/src/utils/DataSourceWithBackend.ts#L207

I was thinking it would be good to have the same name?

[scottlepp]

yeah that makes sense, just confusing

[vickyyyyyyy]

Yeah, I can see how that can be confusing - hopefully the jsdocs I've added can help clarify things

[srclosson]

Any reason why you want to store the response and return it?
Also, why await? You are returning a promise anyway or an error.
return baseTestDatasource();

[vickyyyyyyy]

Good point! This was from when I was thinking of transforming things after we receive the response (before I realised we only ever care about the error) 💯