Merge #21205: build: actually fail when Boost is missing

c5da2749e2f7375e292fb0982e8e252ae1adbce3 build: actually stop configure if Boost isn't available (fanquake)
cad8b527eaf7a93877e2249960866fd4db2d1c14 build: explicitly install libboost-dev package (fanquake)

Pull request description:

  If Boost is not found via AX_BOOST_BASE, we don't actually stop
  configuring, only a warning is emitted:
  ```bash
  checking for boostlib >= 1.58.0 (105800)... configure: We could not detect the boost libraries (version MINIMUM_REQUIRED_BOOST or higher). If you have a staged boost library (still not installed) please specify $BOOST_ROOT in your environment and do not give a PATH to --with-boost option.  If you are sure you have boost installed, then check your version number looking in <boost/version.hpp>. See http://randspringer.de/boost for more documentation.
  ```

  Instead we usually fail when one of the other AX_BOOST_* macros fails to find a library. These macros are slowly being
  removed, and in any case, it makes more sense to fail earlier if Boost is missing.

  If Boost is unavailable, the failure now looks like:
  ```bash
  checking for boostlib >= 1.58.0 (105800)... configure: We could not detect the boost libraries (version 1.58.0 or higher). If you have a staged boost library (still not installed) please specify $BOOST_ROOT in your environment and do not give a PATH to --with-boost option.  If you are sure you have boost installed, then check your version number looking in <boost/version.hpp>. See http://randspringer.de/boost for more documentation.
  configure: error: Boost is not available!
  ```

  Note that we now just pass the version into AX_BOOST_BASE, which fixes it's display in the output (rather than showing `MINIMUM_REQUIRED_BOOST`).

  This PR also has a commit that adds `libboost-dev` to our install instructions and CI. This package is currently installed as a side-effect of installing our other libboost-*-dev packages. However as those continue to disappear, it makes sense to install boost-dev explicitly.

ACKs for top commit:
  laanwj:
    Code review ACK c5da2749e2f7375e292fb0982e8e252ae1adbce3
  MarcoFalke:
    Concept ACK c5da2749e2f7375e292fb0982e8e252ae1adbce3

Tree-SHA512: f866062f9d7d3a2316b6c887f17c664b9cfff41fdc0cb99ca79d641240fb01a5ae0d34140e515bc465219e1b43d5ca84f7c55f48b9c5b45a80ff2795dafd072b

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