Merge #193: build: require CapnProto 0.7.0 or better

30930df build: require CapnProto 0.7.0 or better (Sjors Provoost)

Pull request description:

  Although 1.0.1. is the oldest version currently covered by Bitcoin Core's extensive CI, Debian Bookwork ships 0.9.2 and #194 introduces test coverage for even older versions. 0.7 has been required since #88.

  The CI run of Sjors/bitcoin#100 @ [3d55222](https://github.com/Sjors/bitcoin/pull/100/checks?sha=3d552223712eed88d17e5ead1ef7d1ba6fd7e89e) previously checked Bitcoin Core CI against 1.0.1 as the minimum. Lowering the minimum further should not be a problem for that CI.

ACKs for top commit:
  ryanofsky:
    Code review ACK 30930df. Planning to follow up in #194 to actually test minimum version and error if capnproto version detected is affected by CVE-2022-46149

Tree-SHA512: bed5843973c8ff1f0b2bd93efe7169824c2306097efefaace1752efeb06606df765b68b7ef50c07f5d703010c4d1b324099d6780fa0363e126d34ac1307fba1a

Author: ryanofsky

CMakeLists.txt

@@ -12,7 +12,7 @@ endif()
 
 include("cmake/compat_find.cmake")
 
-find_package(CapnProto REQUIRED)
+find_package(CapnProto 0.7.0 REQUIRED)
 find_package(Threads REQUIRED)
 
 set(MPGEN_EXECUTABLE "" CACHE FILEPATH "If specified, should be full path to an external mpgen binary to use rather than the one built internally.")