Setup dates for Yoga combined election

Yoga cycle is going to have combined election.

As per the TC charter:
- TC election needs to be held in between of R6 to R4 week of Xena release
- PTL election needs to be held on or before R3 week.

Ref: https://governance.openstack.org/tc/reference/charter.html

Release dates:
If we combine both election schedule as per TC charter it comes as:
between R6 to R4 week:
R-6: Aug 23
R-4: Sep 10

Ref: https://releases.openstack.org/xena/schedule.html

Change-Id: Ic58a85b83f8178086a3f1721009ddd4af3594e50

configuration.yaml

@@ -1,17 +1,20 @@
 ---
-release: xena
+release: yoga
-election_type: tc
+election_type: combined
-tag: 892c4f3a851428cf41bab57c6c283e82f1df06d8
+tag: oct-2021-elections
-tc_seats: 5
+tc_seats: 4
 timeframe:
-  name: Victoria-Wallaby
+  name: Wallaby-Xena
-  start: 2020-04-24T00:00
+  start: 2020-09-25T00:00
-  end: 2021-03-08T00:00
+  end: 2021-08-24T00:00
-  email_deadline: 2021-03-08T00:00
+  email_deadline: 2021-08-24T00:00
 timeline:
-  - name: TC Vacancy Nominations
+  - name: TC & PTL Nominations
-    start: 2021-03-25T23:45
+    start: 2021-08-17T23:45
-    end: 2021-04-08T23:45
+    end: 2021-08-24T23:45
-  - name: TC Vacancy Election
+  - name: TC Campaigning
-    start: 2021-04-08T23:45
+    start: 2021-08-24T23:45
-    end: 2021-04-15T23:45
+    end: 2021-08-31T23:45
+  - name: TC & PTL Election
+    start: 2021-08-31T23:45
+    end: 2021-09-07T23:45