Adds SendMail for GraphUser or Me

[MathijsVerbeeck]

Issue ref: #895

@jansenbe I have noticed that for sending mails using Me we need to use the Delegated Authentication Flow, otherwise, the Graph API will throw the following error:
{"error":{"code":"BadRequest","message":"/me request is only valid with delegated authentication flow.","innerError":{"date":"2022-06-29T05:59:27","request-id":"b846630d-4c65-4b57-98cf-11a83fa613e5","client-request-id":"b846630d-4c65-4b57-98cf-11a83fa613e5"}}}

[codecov-commenter]

Codecov Report

Merging #905 (a7fb0fe) into dev (63545f3) will increase coverage by 1.43%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##              dev     #905      +/-   ##
==========================================
+ Coverage   82.42%   83.86%   +1.43%     
==========================================
  Files         416      590     +174     
  Lines       28590    38669   +10079     
==========================================
+ Hits        23565    32428    +8863     
- Misses       5025     6241    +1216     

Impacted Files	Coverage Δ
...re/Model/SharePoint/Changes/Internal/ChangeUser.cs	0.00% <0.00%> (-100.00%)	⬇️
...k/PnP.Core/Model/Teams/Internal/TeamChatMessage.cs	72.34% <0.00%> (-27.66%)	⬇️
...odel/Security/Internal/SharePointUserCollection.cs	78.78% <0.00%> (-21.22%)	⬇️
.../SharePoint/Core/Internal/ContentTypeCollection.cs	84.69% <0.00%> (-15.31%)	⬇️
...PnP.Core.Admin/Model/Teams/Internal/TeamCreator.cs	76.19% <0.00%> (-14.29%)	⬇️
src/sdk/PnP.Core/Services/Core/TestManager.cs	54.94% <0.00%> (-12.96%)	⬇️
...k/PnP.Core/Model/SharePoint/Core/Internal/Field.cs	80.18% <0.00%> (-12.68%)	⬇️
...e/Model/Teams/Internal/TeamChannelTabCollection.cs	87.92% <0.00%> (-12.08%)	⬇️
.../Model/SharePoint/Core/Internal/ListItemVersion.cs	66.66% <0.00%> (-11.12%)	⬇️
.../Model/SharePoint/Core/Internal/SharePointAdmin.cs	83.33% <0.00%> (-10.53%)	⬇️
... and 274 more

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