build: bazelisk should be go-get'ed to ./bin

[dt]

Generally go getable tools required by make, like crlfmt or buf are automatically installed in ./bin which make adds to its PATH and most engineers probably add to their PATH as well. It seems like given that running bazel is required to prepare a green patch now (i.e. CI will fail if make bazel-generate was not run, which invokes bazel), we should treat it like other tools that make requires, and GOBIN=./bin go get github.com/bazelbuild/bazelisk it along with all the other build tools, and probably also then symlink bin/bazel to bin/bazelisk?

Epic CRDB-17171

[dt]

cc @rickystewart

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