RI-7574: allow setting default theme from query param

[KrumTy]

Description

For RiC we want to get the theme from SM. The agreed upon approach is to pass it as query param. This PR sets up the handling of such query param. There will be another one for SM that will pass it.

The theme comes from:

1. default is set to RI_DEFAULT_THEME env variable ('SYSTEM' by default)
2. then a localstorage item is checked, under theme key
3. then user settings config is checked, fetched from the /settings endpoint, taking the data from sqlite db. Once this setting is fetched, if the config theme is different than the one in localstorage, an update is triggered to update the localstorage and app state

Now, with this change, I'm adding a step inbetween 1. and 2., call it 1.5 - if theme query param is passed and it contains valid theme key value, that will be used over the default/localstorage value (updating the localstorage in the process). If

For RiC there's no sqlitdb config, the endpoint returns theme:null, hence the 3rd point above will not update the app theme.

For non-RiC (e.g. web/docker build) the query param will only override the default theme, then this state will be overridden by the /settings theme data, should one present. This is just explaining the behaviour, although it's not expected to use the theme query param for these builds.

[KrumTy]

changing theme via changeTheme is the correct approach as it updates the theme provider and calls themeService.applyTheme internally

[valkirilov]

Note: It's not directly related to your changes, but I would suggest putting this "magic string" behind an enum.

We have similar logic in about 15 other places in the codebase where we use the same approach. I believe having a centralized location where we can view a list of all the available query parameters that Redis Insight accepts and handles will be beneficial. It will be both cleaner and also better in terms of self-explanatory "code documentation".

If you find this advice useful, we can log a separate tech debt ticket with low priority and reference it outside the scope of this change.

[github-actions]

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