Migrate from entry unique id to emoncms unique id (#129133)

* Migrate from entry unique id to emoncms unique id

* Use a placeholder for the documentation URL

* Use async_set_unique_id in config_flow

* use _abort_if_unique_id_configured in config_flow

* Avoid single-use variable

Co-authored-by: epenet <6771947+epenet@users.noreply.github.com>

* Add async_migrate_entry

* Remove commented code

* Downgrade version if user add server without uuid

* Improve code quality

* Move code migrating HA to emoncms uuid to init

* Fit doc url in less than 88 chars

Co-authored-by: epenet <6771947+epenet@users.noreply.github.com>

* Improve code quality

* Only update unique_id with async_update_entry

Co-authored-by: epenet <6771947+epenet@users.noreply.github.com>

* Make emoncms_client compulsory to get_feed_list

* Improve readability with unique id functions

* Rmv test to give more sense to _migrate_unique_id

---------

Co-authored-by: epenet <6771947+epenet@users.noreply.github.com>

tests/components/emoncms/test_config_flow.py

@@ -142,3 +142,21 @@ async def test_options_flow_failure(
     assert result["description_placeholders"]["details"] == "failure"
     assert result["type"] is FlowResultType.FORM
     assert result["step_id"] == "init"
+
+
+async def test_unique_id_exists(
+    hass: HomeAssistant,
+    mock_setup_entry: AsyncMock,
+    emoncms_client: AsyncMock,
+    config_entry_unique_id: MockConfigEntry,
+) -> None:
+    """Test when entry with same unique id already exists."""
+    config_entry_unique_id.add_to_hass(hass)
+    result = await hass.config_entries.flow.async_init(
+        DOMAIN, context={"source": SOURCE_USER}
+    )
+    result = await hass.config_entries.flow.async_configure(
+        result["flow_id"], USER_INPUT
+    )
+    assert result["type"] is FlowResultType.ABORT
+    assert result["reason"] == "already_configured"