Activity as standard object (#6219)

In this PR I layout the first steps to migrate Activity to a traditional
Standard objects

Since this is a big transition, I'd rather split it into several
deployments / PRs

<img width="1512" alt="image"
src="https://github.com/user-attachments/assets/012e2bbf-9d1b-4723-aaf6-269ef588b050">

---------

Co-authored-by: Charles Bochet <charles@twenty.com>
Co-authored-by: bosiraphael <71827178+bosiraphael@users.noreply.github.com>
Co-authored-by: Weiko <corentin@twenty.com>
Co-authored-by: Faisal-imtiyaz123 <142205282+Faisal-imtiyaz123@users.noreply.github.com>
Co-authored-by: Prateek Jain <prateekj1171998@gmail.com>

packages/twenty-server/src/engine/api/__mocks__/object-metadata-item.mock.ts

@@ -189,6 +189,13 @@ const fieldRawJsonMock = {
   defaultValue: null,
 };
 
+const fieldRichTextMock = {
+  name: 'fieldRichText',
+  type: FieldMetadataType.RICH_TEXT,
+  isNullable: true,
+  defaultValue: null,
+};
+
 export const fields = [
   fieldUuidMock,
   fieldTextMock,
@@ -210,6 +217,7 @@ export const fields = [
   fieldPositionMock,
   fieldAddressMock,
   fieldRawJsonMock,
+  fieldRichTextMock,
 ];
 
 export const objectMetadataItemMock = {