Offchain-worker: Make it possible to disable http support (#10087)

* Offchain-worker: Make it possible to disable http support

If a chain doesn't require http support in its offchain workers, this pr enables them to disable the
http support.

* Switch to bitflags

* Use Capabilities

* Update client/offchain/src/lib.rs

Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* Fix test

* Update client/offchain/src/lib.rs

Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

substrate/Cargo.lock

@@ -8184,6 +8184,7 @@ dependencies = [
  "lazy_static",
  "log 0.4.14",
  "num_cpus",
+ "once_cell",
  "parity-scale-codec",
  "parking_lot 0.11.1",
  "rand 0.7.3",
@@ -9232,6 +9233,7 @@ name = "sp-core"
 version = "4.0.0-dev"
 dependencies = [
  "base58",
+ "bitflags",
  "blake2-rfc",
  "byteorder",
  "criterion",