docs: clarify that support schedule is subject to change (#40770)
docs: clarify that support schedule is subject to change (#40770)

Initially raised due to #39509, this change updates our
"Support policy and schedule" with the same disclaimer
from the "Release frequency" section above.

PR Close #40770

gnomeontherun/angular,gkalpak/angular,mgechev/angular,JiaLiPassion/angular,alxhub/angular,brandonroberts/angular,alxhub/angular,ocombe/angular,mgechev/angular,brandonroberts/angular,mgechev/angular,JiaLiPassion/angular,mgechev/angular,brandonroberts/angular,gkalpak/angular,brandonroberts/angular,shairez/angular,ocombe/angular,JiaLiPassion/angular,alxhub/angular,gkalpak/angular,brandonroberts/angular,manekinekko/angular,manekinekko/angular,manekinekko/angular,manekinekko/angular,manekinekko/angular,ocombe/angular,shairez/angular,angular/angular,mgechev/angular,ocombe/angular,angular-indonesia/angular,alxhub/angular,manekinekko/angular,angular-indonesia/angular,JiaLiPassion/angular,alxhub/angular,angular-indonesia/angular,angular/angular,angular-indonesia/angular,angular/angular,gnomeontherun/angular,gnomeontherun/angular,brandonroberts/angular,gkalpak/angular,shairez/angular,shairez/angular,ocombe/angular,shairez/angular,gnomeontherun/angular,angular/angular,ocombe/angular