Bump version numbers and dates for 1.7.3/Ulpian release.

.github/workflows/main.yml

.jenkins.groovy

general/docs/changelogs/ch1_7_3.md

general/docs/changelogs/gh-1_7_3.jq

pom.xml

tlatools/org.lamport.tlatools/github.xml

tlatools/org.lamport.tlatools/ossrh.xml

tlatools/org.lamport.tlatools/pom.xml

tlatools/org.lamport.tlatools/src/tlc2/TLCGlobals.java

toolbox/org.lamport.tla.toolbox.doc/pom.xml

...t.product/org.lamport.tla.toolbox.product.product.product

...box/org.lamport.tla.toolbox.product.standalone/plugin.xml

...rc/org/lamport/tla/toolbox/ui/intro/ToolboxIntroPart.java