Legg til manglende indeksfil for at deploy ikke skal feile

[magnusrand]

Deploy to staging gir følgende feil:

	[invites.receiver] -- (ASCENDING) (DESCENDING) (CONTAINS) (ASCENDING)
? Would you like to delete these field overrides? Selecting no will continue the
 rest of the deployment. (y/N) ? Would you like to delete these field overrides? Selecting no will continue the
 rest of the deployment. (y/N) ? Would you like to delete these field overrides? Selecting no will continue the
 rest of the deployment. (y/N) 

Too long with no output (exceeded 10m0s): context deadline exceeded

Denne PRen legger til filen som beskriver indeksen opprettet i firebase console slik at man ikke får spørsmål om man ønsker å overskrive dataen.

Testet ved å kjøre firebase deploy -P staging --only firestore:indexes, og dette fungerte uten problemer.