CI: Go 1.21.0 + default.pgo

[vadimalekseev]

Bump Go 1.21.0 and paste default.pgo to enable pgo

[zamazan4ik]

@vadimalekseev Do you have performance benefits numbers from enabling PGO on file.d? If yes, could you please share the measured performance numbers? Another question - from which workload is the default.pgo file collected? We are trying to estimate - Do we need to prepare our own PGO profile or we can use the distributed with file.d one?

Thanks in advance!