examples: Rename 18_ota to 26_ota

example numbers should accord with our internal definition.

diff --git a/examples/18_ota/Makefile b/examples/26_ota/Makefile
similarity index 100%
rename from examples/18_ota/Makefile
rename to examples/26_ota/Makefile

diff --git a/examples/18_ota/OTA_workflow.png b/examples/26_ota/OTA_workflow.png
similarity index 100%
rename from examples/18_ota/OTA_workflow.png
rename to examples/26_ota/OTA_workflow.png

diff --git a/examples/18_ota/README.md b/examples/26_ota/README.md
similarity index 100%
rename from examples/18_ota/README.md
rename to examples/26_ota/README.md

diff --git a/examples/18_ota/main/Kconfig.projbuild b/examples/26_ota/main/Kconfig.projbuild
similarity index 100%
rename from examples/18_ota/main/Kconfig.projbuild
rename to examples/26_ota/main/Kconfig.projbuild

diff --git a/examples/18_ota/main/component.mk b/examples/26_ota/main/component.mk
similarity index 100%
rename from examples/18_ota/main/component.mk
rename to examples/26_ota/main/component.mk

diff --git a/examples/18_ota/main/ota.c b/examples/26_ota/main/ota.c
similarity index 100%
rename from examples/18_ota/main/ota.c
rename to examples/26_ota/main/ota.c

diff --git a/examples/18_ota/sdkconfig.defaults b/examples/26_ota/sdkconfig.defaults
similarity index 100%
rename from examples/18_ota/sdkconfig.defaults
rename to examples/26_ota/sdkconfig.defaults