fix: avoid layer reloads and redrawing the map

[turban]

This PR fixes issues to avoid expensive reloads of map layers and map redraws:

• System setting keyDefaultBaseMap is not always available when we first load/render a map. We wait for the value before we fetch the map (so we don't trigger the fetch twice).
• If a map has more than one layer, and one layer finishes loading before the other, the new load is triggered for the unloaded layers. This PR adds a new isLoading prop to the layer config. If true it will not trigger a new load of the layer.

After this PR the thematic loaded is only triggered once for a map with two thematic layers:

Before the thematic loaded was triggered 5 times (3 is not needed):

[cypress]

Passing run #1870 ↗︎

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Details:

fix: avoid interpretation map redraws (#2531)
Project: maps	Commit: d5449f5761
Status: Passed	Duration: 04:23 💡
Started: Mar 16, 2023 9:35 AM	Ended: Mar 16, 2023 9:40 AM

_{This comment has been generated by cypress-bot as a result of this project's GitHub integration settings.}

[dhis2-bot]

🎉 This PR is included in version 1.30.15 🎉

The release is available on GitHub release

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