Availability: provisioner bitfield metrics (#5484)

* Add histogram for inherent data bitfields

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

* -500ms bitfield sign job delay, +500ms bitfield gossip

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

* Revert "-500ms bitfield sign job delay, +500ms bitfield gossip"

This reverts commit 3d3f2c0fae651653ffdca50c1ad38c5757166edc.

* fmt

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

* Update node/core/provisioner/src/metrics.rs

Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

Co-authored-by: Andronik <write@reusable.software>
Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>