Release 5.1.0

[petmongrels]

1. Fix all duplicate form mappings (see sql here)
2. Fix duplicate media images issue as part of Fix duplicate images with respect to data avni-server#634 (comment) on Prod DB for all affected organisations
3. Send mail to client with approximate server downtime info
4. Add export AVNI_LEGACY_LONGITUDINAL_EXPORT_LIMIT=30000 in /etc/openchs/openchs.conf
5. Follow this readme: https://avni.readme.io/docs/release-process-for-the-cloud
6. After releasing the app to open testing track wait for 2 days for the clients to test
7. Merge repositories - client, server, models, webapp
8. Tag the commits on release branch with the release version. Or make sure by tagging the release notes this is achieved.
9. Execute script on this: Write and execute update SQL to cater to change in subject migration logic avni-server#647 once the QA for it is done.

[1t5j0y]

[Info]
For step 1, 8 duplicate form mappings were present which all belonged to UAT or archived orgs.
For step 2, 26 individual and 37 encounter media dupes were present before running dedupe query.

[Discussion]
Step 8 seems erroneous. Needs discussion if this should be done.

[Pending]
Step 9 - Card not QAd yet.

[1t5j0y]

Discussed step 8 and description changed to tags on release and not on master.