Add prometheus registry to transaction pool, with couple of initial metrics (#5657)

* make new contructor

* add metrics to txpool

* fix review

* fix doc comment

* change to counters

* Update client/transaction-pool/src/metrics.rs

Co-Authored-By: Max Inden <mail@max-inden.de>

* Update client/transaction-pool/src/metrics.rs

Co-Authored-By: Max Inden <mail@max-inden.de>

* Update client/transaction-pool/src/metrics.rs

Co-Authored-By: Max Inden <mail@max-inden.de>

* Update client/transaction-pool/src/lib.rs

Co-Authored-By: Max Inden <mail@max-inden.de>

* Update client/transaction-pool/src/lib.rs

Co-Authored-By: Max Inden <mail@max-inden.de>

* use dedicated wrapper

Co-authored-by: Max Inden <mail@max-inden.de>