Implement in gerrit tree Bazel build

"Implementation-Vendor" manifest file entry is overridden in plugin
implementation in Gerrit core, so we do not provide it now.

Not addressed in this commit:

strip the documentation files form the its-base plugin, to avoid
eclipsing them from the documentation provided by this plugin:

* about.md
* build.md
* config-connectivity.md
* config-rulebase-plugin-actions.md

Change-Id: I4677013e19f82789946f62eaafd2cb9e03417ce8