Optimized Token requirements for Trust Protection Platform

• Updated so the only credential required to initialize with Trust Protection Platform is refresh_token ✨#65
• Renamed plugin binaries for consistency with vault-pki-backend-venafi project; vault-pki-monitor-venafi_strict binary is now venafi-pki-monitor, and vault-pki-monitor-venafi_optional is now venafi-pki-monitor_optional
• Resolved build issue that resulted in the "optional" binaries actually being the "strict" (i.e. policy enforcement was required)
• Added text file containing SHA256 hash to release assets (zip archives); the hash is specified when adding the plugin to the Vault catalog and is currently the only way HashiCorp provides to differentiate plugin versions
• Discontinued darwin 386 (32-bit macOS) releases since support was dropped in Go 1.15 and Vault 1.6.0

0c58f0227f113e94fb4b9e6cccc806f2629feea6d97be137af4b89539c2b6230  venafi-pki-monitor_v0.8.2_darwin_optional.zip
a9fc94b28bf98aa5d241bff900d75b022ea7e5a92e023962cff7e3703c4bdbb5  venafi-pki-monitor_v0.8.2_darwin_strict.zip
74812bc9c1e0d3069fa675bf9e2958f6a8b1a7d3590edb2e03951e47e6dd62b5  venafi-pki-monitor_v0.8.2_linux86_optional.zip
d748308676ab04b3c465bc1ee4f05c2cb802bddd0ab8773493ad84f5a2410f4d  venafi-pki-monitor_v0.8.2_linux86_strict.zip
099344e2b3bb113f827badedd36490ee81222a842dfa3d1a9f379f49491af7f8  venafi-pki-monitor_v0.8.2_linux_optional.zip
1e3a347868a333d2d22f60d55f17eddc6726a96e9d2a4766256f35bf1363472f  venafi-pki-monitor_v0.8.2_linux_strict.zip
6b68b3ba62419b992d855734ef4c940008f17b4cc10ed333cd0ef418d733ef83  venafi-pki-monitor_v0.8.2_windows86_optional.zip
9003ddbe56d48fa012372484f4ab1c8b28866b24f89f56ddcbfb054563b1df99  venafi-pki-monitor_v0.8.2_windows86_strict.zip
11ba652095dc130bc39ff6745026cfa9cf708b129ca31135bd824c35680d0b03  venafi-pki-monitor_v0.8.2_windows_optional.zip
0e9f2eecf9530c8404df0d2bee9ca0362744ea0892e0ef897a02912a6df1bc27  venafi-pki-monitor_v0.8.2_windows_strict.zip