[RN 7.0] Adds Heat known issue
[RN 7.0] Adds Heat known issue

This patch adds Heat known bug description
to the MOS Resolved and Known Issues section
of Release Notes 7.0 page.

Change-Id: I2b53cffb3f422f762278400a50a5cf74ec05dc72
Related-Bug: #1497273

stackforge/fuel-docs,stackforge/fuel-docs