Measurement of the production cross section for <math display='"inline"'> <mrow> <mi>Z</mi> <mo>+</mo> <mi>b</mi> </mrow> </math> jets in proton-proton collisions at <math display='"inline"'> <mrow> <msqrt> <mrow> <mi>s</mi> </mrow> </msqrt> <mo>=</mo> <mn>1</mn></mrow></math>