docs(migration): Add migration guide for 6 to 7

documentation/migration-guide.json

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+{
+  "title": "Migration guide",
+  "description": "This guide provides help on how to migrate from one major version to another",
+  "order": 8,
+  "tags": ["guideline", "how to", "tutorial", "upgrade", "major version"]
+}

documentation/migration-guide.md

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+# Migration guide
+
+## Migrate from v6 to v7
+
+### Highcharts
+
+For the major version upgrade to 7.0.0 we bumped the version of the peer
+dependency `highcharts` to use version `^7.0.0`. This version of highcharts is
+the first version that comes with official typings for typescript. Previously we
+had to use community typings that were outdated. This upgrade requires some
+manual changes to be performed for those typings.
+
+Most common typings from the previous version:
+
+#### SeriesOptions
+
+If you used `SeriesOptions` before, please use `Options` from highcharts or
+`DtChartOptions` for the options part of the configuration.
+
+#### IndividualSeriesOptions
+
+If you used `IndividualSeriesOptions` before, please either use the
+`DtChartSeries` type or use one of the types used in the union if you can be
+more explicit, e.g. `SeriesBarOptions`, `SeriesColumnOptions`,
+`SeriesLineOptions`, `SeriesAreaOptions`, `SeriesArearangeOptions`,
+`SeriesPieOptions`. The `dt-chart` does not support other chart types.
+
+#### DataPoint
+
+If you used the `DataPoint` type before, in most cases the new type that fits in
+highcharts 7 is `PointOptionsObject`.
+
+### lodash -> lodash-es
+
+We switched the peer dependency of `lodash` to `lodash-es` to enable treeshaking
+and reduce our bundle size. Our advice would be to also switch to `lodash-es`
+for your app. If you are using jest as a testrunner as we do and encounter
+problems with `lodash-es` because it does not ship commonjs bundles, you can add
+the following snippet to your `jest.config.js`.
+
+```js
+  moduleNameMapper: {
+    // map lodash-es to lodash bundle since jest needs commonjs
+    '^lodash-es$': 'node_modules/lodash/index.js',
+  },
+```
+
+Note: You need to have `lodash` installed as a dev dependency as well, since
+jest will take the lodash version for all `lodash-es` imports in your code.
+
+### Filter field
+
+We improved the typings for our `DtFilterFieldDefaultDatasource` class. The
+class is not a generic class anymore. Please remove the generic type and verify
+that your code is compatible with our default datasource implementation. If you
+want to use your own types for the filter field please create your own
+datasource.