Add linter rule to avoid floating promises

[sameerag]

Adding a linter rule to avoid floating promises: no-floating-promises

Note: Thanks @peterzenz for spotting this and @konstantin-msft for the linter tip.

[codecov-commenter]

Codecov Report

Merging #6421 (b61203f) into dev (81d34b4) will decrease coverage by 2.06%.
Report is 289 commits behind head on dev.
The diff coverage is 61.03%.

Flag	Coverage Δ
msal-angular	96.73% <ø> (+0.22%)	⬆️
msal-browser	85.24% <ø> (-1.23%)	⬇️
msal-common	82.85% <ø> (-1.70%)	⬇️
msal-core	?
msal-node	80.01% <ø> (-3.38%)	⬇️
msal-node-extensions	68.51% <60.77%> (-7.13%)	⬇️
msal-react	94.24% <ø> (-0.45%)	⬇️
node-token-validation	?

Files Changed	Coverage Δ
...ions/msal-node-extensions/src/utils/Environment.ts	20.51% <0.00%> (-22.08%)	⬇️
lib/msal-angular/src/constants.ts	100.00% <ø> (ø)
lib/msal-angular/src/msal.broadcast.service.ts	100.00% <ø> (ø)
lib/msal-angular/src/msal.guard.ts	90.78% <ø> (+0.64%)	⬆️
lib/msal-angular/src/msal.interceptor.ts	100.00% <ø> (ø)
lib/msal-angular/src/msal.module.ts	100.00% <ø> (ø)
lib/msal-angular/src/msal.navigation.client.ts	93.33% <ø> (+0.47%)	⬆️
lib/msal-angular/src/msal.redirect.component.ts	100.00% <ø> (ø)
lib/msal-angular/src/msal.service.ts	100.00% <ø> (ø)
lib/msal-angular/src/packageMetadata.ts	100.00% <ø> (ø)
... and 55 more

... and 178 files with indirect coverage changes