Docs: Additional 7.3 upgrade notes (#28592)

Adds a couple upgrade notes for v7.3 regarding database migrations for 
user invites and snapshots.

Co-authored-by: Will Browne <wbrowne@users.noreply.github.com>

docs/sources/installation/upgrading.md

@@ -297,4 +297,21 @@ The other authentication methods, _Access & secret key_ and _Credentials file_,
 
 For more information and details, please refer to [Using AWS CloudWatch in Grafana]({{< relref "../datasources/cloudwatch.md#authentication" >}}).
 
-<!-- BEGIN Optimal Workshop Intercept Snippet --><div id='owInviteSnippet' style='position:fixed;right:20px;bottom:20px;width:280px;padding:20px;margin:0;border-radius:6px;background:#1857B8;color:#F7F8FA;text-align:left;z-index:2200000000;opacity:0;transition:opacity 500ms;-webkit-transition:opacity 500ms;display:none;'><div id='owInviteMessage' style='padding:0;margin:0 0 20px 0;font-size:16px;'>Got a spare two and a half minutes to help us improve the docs?</div><a id='owInviteOk' href='https://Grafana.optimalworkshop.com/questions/grafana-docs?tag=docs&utm_medium=intercept' onclick='this.parentNode.style.display="none";' target='_blank' style='color:#F7FAFF;font-size:16px;font-weight:bold;text-decoration:underline;'>Yes, I&#x27;ll help</a><a id='owInviteCancel' href='javascript:void(0)' onclick='this.parentNode.style.display="none";' style='color:#F7F8FA;font-size:14px;text-decoration:underline;float:right;'>Close</a></div><script>var owOnload=function(){if(-1==document.cookie.indexOf('ow-intercept-quiz-4ior230e')){var o=new XMLHttpRequest;o.onloadend=function(){try{var o=document.getElementById('owInviteSnippet');var date=new Date();date.setMonth(date.getMonth()+1);this.response&&JSON.parse(this.response).active===!0&&(document.cookie='ow-intercept-quiz-4ior230e=Done;path=/;expires='+date.toUTCString()+';',setTimeout(function(){o.style.display='block',o.style.opacity=1},2e3))}catch(e){}},o.open('POST','https://app.optimalworkshop.com/survey_status/questions/4ior230e/active'),o.send()}};if(window.addEventListener){window.addEventListener('load',function(){owOnload();});}else if(window.attachEvent){window.attachEvent('onload',function(){owOnload();});}</script><!-- END Optimal Workshop snippet -->
\ No newline at end of file
+### User invites database migration
+
+The database table _temp\_user_, that tracks user invites, is subject to a database migration that changes the data type of the _created_ and _updated_ columns:
+
+| Database | Old data type | New data type |
+| -------- | ------------- | ------------- |
+| Sqlite   | DATETIME      | INTEGER       |
+| MySQL    | DATETIME      | INT           |
+| Postgres | TIMESTAMP     | INTEGER       |
+
+> Please note that if downgrading Grafana to an earlier version, you have to manually change the data type of the _created_ and _updated_ columns back to _old data type_ , otherwise the user invite feature doesn't function as expected.
+
+### Snapshots database migration
+
+The database table _dashboard\_snapshot_, that stores dashboard snapshots, adds a new column _dashboard\_encrypted_ for storing an encrypted snapshot. 
+NOTE: Only snapshots created on Grafana 7.3 or later will use this column to store snapshot data as encrypted. Snapshots created before this version will be unaffected and remain unencrypted.
+
+<!-- BEGIN Optimal Workshop Intercept Snippet --><div id='owInviteSnippet' style='position:fixed;right:20px;bottom:20px;width:280px;padding:20px;margin:0;border-radius:6px;background:#1857B8;color:#F7F8FA;text-align:left;z-index:2200000000;opacity:0;transition:opacity 500ms;-webkit-transition:opacity 500ms;display:none;'><div id='owInviteMessage' style='padding:0;margin:0 0 20px 0;font-size:16px;'>Got a spare two and a half minutes to help us improve the docs?</div><a id='owInviteOk' href='https://Grafana.optimalworkshop.com/questions/grafana-docs?tag=docs&utm_medium=intercept' onclick='this.parentNode.style.display="none";' target='_blank' style='color:#F7FAFF;font-size:16px;font-weight:bold;text-decoration:underline;'>Yes, I&#x27;ll help</a><a id='owInviteCancel' href='javascript:void(0)' onclick='this.parentNode.style.display="none";' style='color:#F7F8FA;font-size:14px;text-decoration:underline;float:right;'>Close</a></div><script>var owOnload=function(){if(-1==document.cookie.indexOf('ow-intercept-quiz-4ior230e')){var o=new XMLHttpRequest;o.onloadend=function(){try{var o=document.getElementById('owInviteSnippet');var date=new Date();date.setMonth(date.getMonth()+1);this.response&&JSON.parse(this.response).active===!0&&(document.cookie='ow-intercept-quiz-4ior230e=Done;path=/;expires='+date.toUTCString()+';',setTimeout(function(){o.style.display='block',o.style.opacity=1},2e3))}catch(e){}},o.open('POST','https://app.optimalworkshop.com/survey_status/questions/4ior230e/active'),o.send()}};if(window.addEventListener){window.addEventListener('load',function(){owOnload();});}else if(window.attachEvent){window.attachEvent('onload',function(){owOnload();});}</script><!-- END Optimal Workshop snippet -->