Add files from research-template repository

See #29.

These were in the `research-template` but we intend to store them here
to simplify maintenance.

These were taken from
opensafely/research-template@5bd648f.

Note that the `postAttach.sh` only existed as a line in the `devcontainer.json`
and has now been moved to a script.

devcontainer/postAttach.sh

@@ -0,0 +1,2 @@
+#!/bin/bash
+sudo rstudio-server start

devcontainer/postCreate.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+
+set -euo pipefail 
+
+/usr/local/bin/pip3 install --user -r .devcontainer/requirements.in
+
+#set R working directory
+! grep -q "$1" $R_HOME/etc/Rprofile.site && sudo tee -a $R_HOME/etc/Rprofile.site <<< "setwd(\"$1\")"
+#set RStudio working directory
+! grep -q "$1" ~/.config/rstudio/rstudio-prefs.json && cat ~/.config/rstudio/rstudio-prefs.json | jq ". + {\"initial_working_directory\":\"$1\"}" >  ~/.config/rstudio/rstudio-prefs.json 
+
+#download and extract latest ehrql source
+wget https://github.com/opensafely-core/ehrql/archive/main.zip -P .devcontainer
+unzip -o .devcontainer/main.zip -d .devcontainer/
+rm .devcontainer/main.zip

devcontainer/requirements.in

@@ -0,0 +1 @@
+opensafely