QA-1190: Use postgresql client v15 (#8974)

* Use postgresql client v15

* Update README to indicate support for PostgreSQL 15

---------

Co-authored-by: Jordan Krage <jmank88@gmail.com>

README.md

@@ -37,7 +37,7 @@ regarding Chainlink social accounts, news, and networking.
    - Example Path for macOS `export PATH=$GOPATH/bin:$PATH` & `export GOPATH=/Users/$USER/go`
 2. Install [NodeJS v16](https://nodejs.org/en/download/package-manager/) & [pnpm via npm](https://pnpm.io/installation#using-npm).
    - It might be easier long term to use [nvm](https://nodejs.org/en/download/package-manager/#nvm) to switch between node versions for different projects. For example, assuming $NODE_VERSION was set to a valid version of NodeJS, you could run: `nvm install $NODE_VERSION && nvm use $NODE_VERSION`
-3. Install [Postgres (>= 11.x and < 15.x)](https://wiki.postgresql.org/wiki/Detailed_installation_guides).
+3. Install [Postgres (>= 11.x and <= 15.x)](https://wiki.postgresql.org/wiki/Detailed_installation_guides).
    - You should [configure Postgres](https://www.postgresql.org/docs/12/ssl-tcp.html) to use SSL connection (or for testing you can set `?sslmode=disable` in your Postgres query string).
 4. Ensure you have Python 3 installed (this is required by [solc-select](https://github.com/crytic/solc-select) which is needed to compile solidity contracts)
 5. Download Chainlink: `git clone https://github.com/smartcontractkit/chainlink && cd chainlink`

core/chainlink.Dockerfile

@@ -27,7 +27,7 @@ RUN apt-get update && apt-get install -y ca-certificates gnupg lsb-release curl
 # Install Postgres for CLI tools, needed specifically for DB backups
 RUN curl https://www.postgresql.org/media/keys/ACCC4CF8.asc | apt-key add - \
   && echo "deb http://apt.postgresql.org/pub/repos/apt/ `lsb_release -cs`-pgdg main" |tee /etc/apt/sources.list.d/pgdg.list \
-  && apt-get update && apt-get install -y postgresql-client-14 \
+  && apt-get update && apt-get install -y postgresql-client-15 \
   && apt-get clean all
 
 COPY --from=buildgo /go/bin/chainlink /usr/local/bin/

core/chainlink.goreleaser.Dockerfile

@@ -11,7 +11,7 @@ RUN apt-get update && apt-get install -y ca-certificates gnupg lsb-release curl
 # Install Postgres for CLI tools, needed specifically for DB backups
 RUN curl https://www.postgresql.org/media/keys/ACCC4CF8.asc | apt-key add - \
   && echo "deb http://apt.postgresql.org/pub/repos/apt/ `lsb_release -cs`-pgdg main" |tee /etc/apt/sources.list.d/pgdg.list \
-  && apt-get update && apt-get install -y postgresql-client-14 \
+  && apt-get update && apt-get install -y postgresql-client-15 \
   && apt-get clean all
 
 COPY . /usr/local/bin/